To provide a circulating optical path device capable of forming mutually-crossing three circulating optical paths in a space acquired by etching a silicon substrate.

Light excited by an excitation light source 71 of a light source substrate 40 is condensed on a solid laser medium 51, and laser light is radiated from a light emission point 42 onto the first reflection surface substrate 20, and laser light is radiated in both directions in parallel with a reference plane 11 and a plane PL2 from the second light source 80 provided on the first reflection surface substrate 20, and reflected by utilizing a plurality of reflecting surfaces 21-28 on the first reflection surface substrate 20 and a reflecting surface 41 of the light source substrate 40, and three circulating optical paths LC1-LC3 are formed easily in mutually orthogonal planes.