Abstract: An optical repeating device with a monitoring function comprises first optical propagation means for propagating a lightwave signal through an optical transmission line, second optical propagation means butted against the first optical propagation means, for propagating the lightwave signal, optical branching means provided on a butting face between the first optical propagation means, and the second optical propagation means, and photodetection means. All the means described are assembled into a housing, and integrated therewith. Consequently, it is possible to downsize the optical repeating device with the monitoring function. A large portion of the lightwave signal propagated between the first optical propagation means and the second optical propagation means is allowed to pass through the optical branching means, however, a portion of the lightwave signal is reflected in a given direction by the optical branching means.