The invention is intended to provide a position measuring system for a working machine, which can accurately measure the position of a monitoring point and can ensure high working efficiency even when measurement accuracy of a machine-equipped GPS has changed. A panel computer (45) computes the position of the monitoring point, which is set on an operating mechanism, in a three-dimensional space based on values measured by GPS receivers (43, 44) and angle sensors (21, 22, 23). When measurement accuracy of at least one of at least two GPS receivers lowers, the panel computer (45) corrects the computation for the position of the monitoring point based on a yaw angle measured by a gyroscope (25) for measuring the yaw angle of a machine body.