The present invention provides a novel thiazole derivative useful as a VAP-1 inhibitor, a pharmaceutical agent for the prophylaxis or treatment of VAP-1 associated diseases and the like. A compound represented by the formula (I): €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ R 1 -NH-X-Y-Z€ƒ€ƒ€ƒ€ƒ€ƒ(I) wherein each symbol is as defined in the specification, or a pharmaceutically acceptable salt thereof.