An optical power monitoring apparatus according to an aspect of the present invention has an input optical waveguide, a light receiver, and an output optical waveguide. The input optical waveguide has a light entrance end and a light exit end. The input optical waveguide accepts light from the exterior through the light entrance end and outputs the light from the light exit end. The light receiver absorbs part of the light from the light exit end of the input optical waveguide and transmits the other part of the light. The output optical waveguide has a light entrance end and a light exit end. The output optical waveguide accepts the light transmitted by the light receiver, through the light entrance end, and outputs the light from the light exit end. The light receiver is provided on an optical path from the light exit end of the input optical waveguide to the light entrance end of the output optical waveguide.