[Problem to be solved] There is provided a novel compound that inhibits interaction between murine double minute 2 (Mdm2) protein and p53 protein and exhibits anti-tumor activity. [Solution] The present invention provides an imidazothiazole derivative represented by the following formula (1) having various substituents that inhibits interaction between Mdm2 protein and p53 protein and exhibits anti-tumor activity: wherein R1, R2, R3, R4, R5, R6, R7, Ar1, and Ar2 in formula (1) respectively have the same meanings as defined in the specification.