An optically active 4-phenylthiazole derivative having a thrombopoietin receptor agonist activity and a pharmaceutical composition containing the present compound as an active ingredient are created, and a platelet production regulating agent which can be orally administered is provided.Disclosed is a pharmaceutical composition containing, as an active ingredient, an optically active compound represented by the formula:wherein, R1 is a halogen atom or C1-C3 alkyloxy； R2 is C1-C8 alkyl； R3 is C1-C8 alkyl； R4 and R5 are each independently a fluorine atom or chlorine atom； R6 is C1-C3 alkyl or C1-C3 alkyloxy； * indicates that a carbon atom marked with an asterisk is an asymmetric carbon,a pharmaceutically acceptable salt thereof, or a solvate thereof.
