[Problem] The objective of the present invention is to provide a preparation technique with which excellent stability can be provided while preventing the precipitation of diclofenac and/or a salt thereof even when diclofenac and/or a salt thereof and lactic acid and/or a salt thereof coexist. [Solution] Excellent stability can be provided while preventing the precipitation of diclofenac and/or a salt thereof by using menthol in combination with diclofenac and/or a salt thereof and at least 0.1 wt% of lactic acid and/or a salt thereof.
