In a lost child search system including a parent terminal and a child terminal, the child terminal is provided with: a gyro sensor that measures the angular velocity for identifying the posture of that child terminal; an acceleration sensor that measures the acceleration of that child terminal; a positioning control unit that performs relative positioning of that child terminal based on the identified posture and the measured acceleration; a communication unit that performs data communication via near-field wireless communication using radio waves; an intensity detection unit that detects the radio wave intensity in the near-field wireless communication with the parent terminal; and an intensity decision unit that decides whether or not search for the child terminal is necessary in accordance with the detected intensity information. The acceleration sensor is made to start measuring the acceleration in accordance with the decision result (decision information) by the intensity decision unit.
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