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, R 1 is a halogen atom or C1-C3 alkyloxy； R 2 is C1-C8 alkyl R 3 is C1-C8 alkyl R 4 and R 5 are each independently a fluorine atom or chlorine atom； R 6 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.
