diff --git a/study.go b/study.go
index 87bb18b4..4b199850 100644
--- a/study.go
+++ b/study.go
@@ -180,52 +180,6 @@ func (s *Study) WithContext(ctx context.Context) {
 	s.ctx = ctx
 }
 
-func (s *Study) callRelativeSampler(trialID int) (
-	map[string]interface{},
-	map[string]float64,
-	error,
-) {
-	if s.RelativeSampler == nil {
-		return nil, nil, nil
-	}
-
-	frozen, err := s.Storage.GetTrial(trialID)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	var searchSpace map[string]interface{}
-	if s.definedSearchSpace != nil {
-		searchSpace = s.definedSearchSpace
-	} else {
-		searchSpace, err = IntersectionSearchSpace(s)
-		if err != nil {
-			return nil, nil, err
-		}
-	}
-	if searchSpace == nil {
-		return nil, nil, nil
-	}
-
-	for paramName := range searchSpace {
-		distribution := searchSpace[paramName]
-		if yes, _ := DistributionIsSingle(distribution); yes {
-			delete(searchSpace, paramName)
-		}
-	}
-
-	relativeParams, err := s.RelativeSampler.SampleRelative(s, frozen, searchSpace)
-	if err == ErrUnsupportedSearchSpace {
-		s.logger.Warn("Your objective function contains unsupported search space for RelativeSampler.",
-			fmt.Sprintf("trialID=%d", trialID),
-			fmt.Sprintf("searchSpace=%#v", searchSpace))
-		return nil, nil, nil
-	} else if err != nil {
-		return nil, nil, err
-	}
-	return searchSpace, relativeParams, nil
-}
-
 func (s *Study) runTrial(objective FuncObjective) (int, error) {
 	trialID, err := s.popWaitingTrialID()
 	if err != nil {
@@ -241,19 +195,18 @@ func (s *Study) runTrial(objective FuncObjective) (int, error) {
 			return -1, errCreateNewTrial
 		}
 	}
-	searchSpace, relativeParams, err := s.callRelativeSampler(trialID)
+
+	trial := Trial{
+		Study: s,
+		ID:    trialID,
+	}
+	err = trial.CallRelativeSampler()
 	if err != nil {
 		s.logger.Error("failed to call relative sampler",
 			fmt.Sprintf("err=%s", err))
 		return -1, err
 	}
 
-	trial := Trial{
-		Study:               s,
-		ID:                  trialID,
-		relativeParams:      relativeParams,
-		relativeSearchSpace: searchSpace,
-	}
 	evaluation, objerr := objective(trial)
 	var state TrialState
 	if objerr == ErrTrialPruned {
diff --git a/trial.go b/trial.go
index 9bab3253..a65ec932 100644
--- a/trial.go
+++ b/trial.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"reflect"
 )
 
@@ -97,6 +98,57 @@ func (t *Trial) isFixedParam(name string, distribution interface{}) (float64, bo
 	return internalParam, true, nil
 }
 
+// CallRelativeSampler should be called before evaluate an objective function only 1 time.
+// Please note that this method is public for third party libraries like "Kubeflow/Katib".
+// Goptuna users SHOULD NOT call this method.
+func (t *Trial) CallRelativeSampler() error {
+	if t.Study.RelativeSampler == nil {
+		return nil
+	}
+
+	var err error
+	var searchSpace map[string]interface{}
+	if t.Study.definedSearchSpace != nil {
+		searchSpace = t.Study.definedSearchSpace
+	} else {
+		searchSpace, err = IntersectionSearchSpace(t.Study)
+		if err != nil {
+			return err
+		}
+	}
+	if searchSpace == nil {
+		return nil
+	}
+
+	relativeSearchSpace := make(map[string]interface{}, len(searchSpace))
+	for paramName := range searchSpace {
+		distribution := searchSpace[paramName]
+		if yes, _ := DistributionIsSingle(distribution); yes {
+			continue
+		}
+		relativeSearchSpace[paramName] = distribution
+	}
+
+	frozen, err := t.Study.Storage.GetTrial(t.ID)
+	if err != nil {
+		return err
+	}
+
+	relativeParams, err := t.Study.RelativeSampler.SampleRelative(t.Study, frozen, searchSpace)
+	if err == ErrUnsupportedSearchSpace {
+		t.Study.logger.Warn("Your objective function contains unsupported search space for RelativeSampler.",
+			fmt.Sprintf("trialID=%d", t.ID),
+			fmt.Sprintf("searchSpace=%#v", searchSpace))
+		return nil
+	} else if err != nil {
+		return err
+	}
+
+	t.relativeSearchSpace = searchSpace
+	t.relativeParams = relativeParams
+	return nil
+}
+
 func (t *Trial) isRelativeParam(name string, distribution interface{}) bool {
 	expected, ok := t.relativeSearchSpace[name]
 	if !ok {