To enable measuring a displacement at a predetermined position of a measurement object for a short time at a high accuracy. While a scanning mirror is moved in a first scanning range to cause measurement light to irradiate a measurement position, a first irradiation angle of the scanning mirror at the time the measurement light is emitted to the measurement position is obtained. While a scanning mirror is moved in a second scanning range that covers the first irradiation angle and that is narrower than the first scanning range, and a second irradiation angle at the time the measurement light is emitted to the measurement position is obtained. A light receiver outputs a received-light quantity distribution, and a displacement at the measurement position is measured on the basis of the second irradiation angle and the position in a second direction of the measurement position.