Signal detection system

An object of the present invention is to provide a signal detection system capable of removing noise caused by scattered light or the like and capable of detecting an accurate signal. The problems can be solved by providing a signal detection system including an emitting unit that emits polarized light as measurement light, a retroreflection member that retroreflects the measurement light, and a detecting unit that detects the retroreflected measurement light, in which in the retroreflection member, a reflectance of first polarized light is higher than a reflectance of second polarized light which is polarized light having a property opposite to that of the first polarized light, and at least one of a first condition in which in the measurement light emitted from the emitting unit, an intensity of the first polarized light is higher than an intensity of the second polarized light, or a second condition in which in the detecting unit, a detection sensitivity of the first polarized light is higher than a detection sensitivity of the second polarized light is satisfied.