A photoacoustic wave detecting device (100) comprising a light projecting optical system and a photoacoustic wave detecting system, the light projecting optical system comprising: a light source (10) for emitting excitation light and a light source (10) for emitting excitation light emitted from the light source An internal reflection surface 12 b that reflects the excitation light incident from the excitation light incident surface 12 a by internal reflection, an excitation light emission surface 12 b that transmits the excitation light reflected by the internal reflection surface 12 b to the outside And a prism 12 having a surface 12 c and having a positive refractive power. The photoacoustic wave detection system passes through the prism 12 and the excitation light exit surface 12 c of the prism 12, is reflected by the internal reflection surface 12 b , And a transducer 11a for detecting a photoacoustic wave emitted from the prism 12. The photoacoustic wave detection system is such that the optical path from the excitation light exit surface 12c to the transducer 11a is filled with the prism glass material 13 including the prism 12 There.投光光学系と、光音響波検出系と、を有する光音響波検出装置100であって、投光光学系は、励起光を発する光源10と、光源10から発する励起光を透過により内部に導く励起光入射面12aと、励起光入射面12aより入射した励起光を内部反射により反射する内部反射面12bと、内部反射面12bにて反射した励起光を透過により外部へ射出する励起光射出面12cを有し正の屈折力をもつプリズム12と、を有し、光音響波検出系は、プリズム12と、プリズム12の励起光射出面12cを通過後、内部反射面12bにて反射し、プリズム12から射出した光音響波を検知するトランスデューサ11aと、を有し、光音響波検出系は、励起光射出面12cからトランスデューサ11aまでの光路がプリズム12を含むプリズム硝材13により満たされている。
