An optical power monitor capable of being reduced in size even when designed as a multi-channel monitor, and having a reduced light transmission loss is disclosed. The optical power monitor has two optical fibers provided on the light transmission upstream and downstream sides and having cores, the end surfaces which are opposed to each other with the core optical axes offset from each other, and which are fusion-spliced to each other in a fusion splicing portion, a light reflection surface which faces a portion of the upstream-side optical fiber core end surface offset to protrude from the downstream-side optical fiber core end surface in the fusion splicing portion, and which is provided in the downstream-side optical fiber cladding layer, and a photo-diode positioned opposite from the light reflection surface with respect to the downstream-side optical fiber core. Third-order or fourth-order lights strengthening each other in lights leaked into the downstream-side optical fiber cladding layer from the upstream-side optical fiber core end surface are reflected by the reflection surface provided in the cladding layer and detected with the photo-diode.