A hydrazone derivative of formula [I]: wherein Ring A is aryl or heteroaryl, Ring T is heteroaryl or heterocycle, R1 and R2 are independently hydrogen atom, halogen atom, cycloalkylsulfonyl, etc., R3 and R4 combine each other together with the adjacent nitrogen atom to form substituted or unsubstituted heterocycle, R5 is hydrogen atom, halogen atom, cyano, nitro, tetrazolyl, etc., and R6 is hydrogen atom, etc.; or a pharmaceutically acceptable salt thereof is useful as a glucokinase activation agent.