There is provided a positioning system for a work machine using RTK positioning that uses a satellite positioning system, the positioning system including: a sensor controller that is a calculation unit that calculates a position of an antenna, of the satellite positioning system, disposed in the work machine based on a position of working equipment, of the work machine, aligned with a known reference point PR positioned at a work site; and a monitor controller that is an initialization control unit that outputs a control command that causes a receiver, of the satellite positioning system, that performs positioning calculation by the RTK positioning to execute initialization processing of the positioning calculation in which an integer value bias of each satellite and the position of the antenna of the satellite positioning system are unknown, by using the calculated position of the antenna of the satellite positioning system.