PURPOSE: To save sample preheating time among total testing time and improve working efficiency by overlapping the preheating time for each sample with a shift by a testing time or the sum of a testing time and an arbitrary time.

CONSTITUTION: If a testing time t2 for a sample is not known in advance, the first sample is press-tested after a preheating time of t1 and the testing time t2 is recorded. Then, after the start of the preheating of the second sample, the third sample is preheated in parallel when the first testing time t2 or the first testing time t2 plus an arbitrary time Δt elapsed. The preheating of the forth sample is performed similally. By this, the preheating time for each sample is saved and shortened from the total testing time, and the working efficiency is improved.