PURPOSE: To measure the surface temperature distribution of a working body readily, by synchronizing the scanning period of a scanning mirror with the periodic movement of a body.

CONSTITUTION: A driving signal having a frequency corresponding to the testing frequency is outputted from a driving circuit 17 of a vibration testing machine 16. A driving coil 18 is driven, and a vibration test sample 1' is vibrated in the up and down directions. The driving signal is inputted to a variable horizontal/ vertical scanning signal circuit 9'. The horizontal scanning signals having the same period is shaped. The frequency of the horizontal scanning signal is divided and the vertical scanning signal is shaped. The horizontal scanning signal scans a scanning mirror 3 through a horizontal scanning driving circuit 10. Infrared rays are emitted from the surface of the test sample 1', which is scanned by the scanning mirror 3 and detected by an infrared ray detector 12 through lenses 4 and 5. The result is displayed on a display 15 as the surface temperature distribution data of the test sample 1'.