A positional measurement system, comprising: 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; and a target including a relative position detection unit that detects a relative position of the target as to the mobile robot, 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 and the relative position, and a target-side communication unit that communicates with the mobile robot, wherein, the mobile robot further includes a mobile-robot-side communication unit that communicates with the target-side communication unit, a communication channel quality evaluation unit that evaluates quality of a communication channel between the mobile-robot-side communication unit and the target-side communication unit, and at least four pattern signal output devices (150A - 150D) that output pattern signals (SA - SD) which are different from each other, wherein the pattern signal output devices (150A - 150D) are provided to different positions on the mobile robot, wherein, the target further includes a pattern signal reception device that receives the pattern signals (SA -SD) which are output from the pattern signal output devices (150A - 150D) of the mobile robot, and wherein, the position control unit moves the mobile robot to a position which is a high-precision reception position, where GNSS signals yielding positional measurement precision higher than a first threshold position can be received and which is a high-quality communication position where a communication channel of quality higher than a first threshold quality can be established, wherein, the relative position detection unit calculates distances from the pattern signal reception device to the pattern signal output devices (150A - 150D) of the mobile robot based on the pattern signals (SA -SD) received by the pattern signal reception device when the mobile robot situates at the high-precision reception position and the high-quality communication position, wherein, the relative position of the target is detected, by the relative position detection unit, based on the calculated distances, and wherein, the position of the target is calculated, by the target position calculation unit, based on the calculated position of the mobile robot based on GNSS signals received at the position that is the high-precision reception position and the high-quality communication position, and the relative position. 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; and a target including a relative position detection unit that detects a relative position of the target as to the mobile robot, 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 and the relative position, and a target-side communication unit that communicates with the mobile robot, wherein, the mobile robot further includes a mobile-robot-side communication unit that communicates with the target-side communication unit, a communication channel quality evaluation unit that evaluates quality of a communication channel between the mobile-robot-side communication unit and the target-side communication unit, and at least four pattern signal output devices (150A - 150D) that output pattern signals (SA - SD) which are different from each other, wherein the pattern signal output devices (150A - 150D) are provided to different positions on the mobile robot, wherein, the target further includes a pattern signal reception device that receives the pattern signals (SA -SD) which are output from the pattern signal output devices (150A - 150D) of the mobile robot, and wherein, the position control unit moves the mobile robot to a position which is a high-precision reception position, where GNSS signals yielding positional measurement precision higher than a first threshold position can be received and which is a high-quality communication position where a communication channel of quality higher than a first threshold quality can be established, wherein, the relative position detection unit calculates distances from the pattern signal reception device to the pattern signal output devices (150A - 150D) of the mobile robot based on the pattern signals (SA -SD) received by the pattern signal reception device when the mobile robot situates at the high-precision reception position and the high-quality communication position, wherein, the relative position of the target is detected, by the relative position detection unit, based on the calculated distances, and wherein, the position of the target is calculated, by the target position calculation unit, based on the calculated position of the mobile robot based on GNSS signals received at the position that is the high-precision reception position and the high-quality communication position, and the relative position.