An object is to provide a determination device that determines a state of a terminal end portion of a coated optical fiber at any location of the coated optical fiber. Reflection of test light varies in a reflection amount at each wavelength depending on a situation of the terminal end portion of the coated optical fiber. In other words, if the magnitude of the reflection amount at each wavelength can be known, the situation of the terminal end portion of the coated optical fiber can be estimated. The determination device according to the present invention is configured to make test light having a plurality of wavelengths incident from the optical fiber side and determine the test light based on a light intensity ratio of each reflected light beams reflected at the terminal end. In addition, reflection of test light varies in return loss at each wavelength depending on a situation of the terminal end portion of the coated optical fiber. If Rayleigh backscattered light can also be measured when measuring a reflection amount, the return loss can be known for each wavelength, and the situation of the terminal end portion of the coated optical fiber can be estimated from the result. The determination device according to the present invention is configured to make test light having a plurality of wavelengths incident from the optical fiber side and determine the test light based on a return loss at the terminal end.