To attempt to improve the reliability and efficiency of the measurement by using a holder which does not interrupt the optical path of an illumination light and holds the acoustic contact condition with sample constant when the light absorption is measured by the acoustic signal generated by the light absorption of sample.

A sample 3 such as a thin film on a glass board generates an acoustic signal by the volumetric change caused by the light absorption of the sample 1 by illuminating a pulse laser. The sample 3 is inserted into a holder H in which liquid (matching material) 4 is fully filled and which is provided at a sample holder 1. Since the light receiving site of the sample 3 is disposed out of the holder H, the optical path is not interrupted. An acoustic detector 6 such as a piezoelectric element is connected to the holder 1 to detect the signal, and to measures it as the light absorption. The liquid 4 is so supplied into the holder H as to hold the level in the holder H constant. At this time, it is desirable to be at a predetermined temperature. Thus, the acoustic contact condition of the sample 3 with the holder 1 is held constant, and the reliability and accuracy of the measurement are improved. The unnecessary overflowed liquid 10 is introduced into a liquid container 2 for reused.