A controller of a hardness tester can determine, in a condition where a driver is not in operation and when a spring displacement detector and an arm displacement detector detect an amount of displacement of respective objects (plate spring and loading arm), that a loading arm and a plate spring are deformed according to changes in environmental temperature. A favorable hardness test can be performed by the hardness tester corresponding to the environmental temperature according to the determination by carrying out an initialization process that resets the displacement amount of respective object to zero, the displacement amount detected by the spring displacement detector and the arm displacement detector respectively.