The present invention provides a hardness tester capable of accurately detecting a point where an indenter contacts a sample in instrumented indentation testing. Prior to beginning measurement, the hardness tester defines an expected range for a value for a displacement, speed, or acceleration of an indenter during a process of approaching a sample. After measurement has begun, the hardness tester measures the value for the displacement, speed, or acceleration of the indenter during the process of approaching the sample. When the measured value is not within the expected range, the hardness tester determines that detection of a zero point has failed.