To detect a state of a lubricating oil in a refrigerating cycle with satisfactory accuracy by using a compact and low-cost detector.

The state detector for the lubricating oil in the refrigerating cycle is provided with a plurality of optical fibers 15, 16A, 16B and so on which are installed in parallel inside fixation members 14 of an airtight and pressure- resistant structure, light sources 17 and light receiving parts 18A, 18B and so on which are connected to the optical fibers 15, 16A, 16B and so on and decision means 19 which decide the state of the lubricating oil on the basis of beams of light received by the light receiving parts 18A, 18B and so on. The state detector is constituted in such a way that beams of light from the light sources 17 are irradiated at the lubricating oil via the optical fibers 15 and that light from a coloring agent added to the lubricating oil is received by the light receiving parts 18A, 18B and so on via the optical fibers 16A, 16B and so on.