OPTICAL POWER MONITORING DEVICE, LASER DEVICE, AND LASER SYSTEM

An optical power monitoring device of the present invention is an optical power monitoring device which monitors the power of reflected beams input to an optical fiber among reflected beams of outputbeams output from the optical fiber, and is provided with: a photodetector which is disposed near the optical fiber and detects a Rayleigh scattered beam from beams guided by the optical fiber; and acalculating unit which performs calculation for excluding a component corresponding to the output of the output beams from the detection result obtained from the optical detector, by using first information indicating a relationship between an output of the output beams obtained in advance in a situation where the reflected beams are not generated and a detection result of the photodetector. 本发明的光功率监视装置对从光纤输出的输出光的反射光中的输入至上述光纤的反射光的功率进行监视，所述光功率监视装置具备：光检测器，其配置于上述光纤的附近，对被上述光纤导波的光的瑞利散射光进行检测；和运算部，其进行使用表示在不产生上述反射光的状况下预先获得的上述输出光的输出与上述光检测器的检测结果的关系的第信息从通过上述光检测器获得的检测结果除去与上述输出光的输出对应的成分的运算。