A positional measurement system includes: a mobile robot including a global navigation satellite system (GNSS) signal reception unit that receives GNSS signals and calculates a position of the mobile robot based on the GNSS signals, a GNSS signal precision evaluation unit that evaluates positional measurement precision by the received GNSS signals, and a position control unit that moves the mobile robot to a high-precision reception position, where GNSS signals yielding positional measurement precision higher than a first threshold precision can be received; a relative position detection unit that detects a relative position of a target as to the mobile robot situated at the high-precision reception position; and a target position calculation unit that calculates a position of the target based on the calculated position of the mobile robot based on the GNSS signals received at the high-precision reception position, and the relative position.