A low-cost laser power sensor having sufficient measurement accuracy with respect to received light intensity of the power sensor. The power sensor has a sensor substrate which receives monitor light, and a filter which attenuates the intensity of the laser beam before being received by the sensor substrate. The filter is constituted from a material having a laser transmissivity equal to zero, and has a plurality of openings within an irradiation range where the monitor light is irradiated. A summation of opening areas of the openings is equal to or more than 50% of the irradiation range. A part of the laser beam, which is irradiated to the filter and passes through the openings, is directly received by the sensor substrate.