The purpose of the present invention is to provide a compound that has excellent CDK 4/6 inhibitory activity. The present invention is a compound represented by formula (I) or a pharmaceutically acceptable salt of the compound.本發明之目的為提供具有優良之CDK4/6阻礙活性的化合物。 本發明為式(I)表示之化合物或其藥學上所容許之鹽。