Problems, which occur when printing is performed on the surface of a rotating disk using by using a print head arranged in the outer circumferential direction from the center of rotation, are resolved. Light emitting sections performs exposure in synchronism with rotational driving for rotating a medium, and pixels which are adjacent in the circumferential direction of rotation are exposed in a partially superimposed fashion by making the amount of movement in the circumferential direction along which the outermost circumference of the medium moves between exposures smaller than the width in the circumferential direction of the pixels formed by exposure. In a plurality of light emitting sections provided in an optical unit, the quantity of light for exposing a pixel on the inner circumferential side in the radial direction is set to be smaller than the quantity of light for exposing a pixel on the outer circumferential side in the radial direction for the respective exposure positions for the medium. Therefore, difference in the tonal shading caused by superposition is reduced by lowering the density created by each exposure in respect of the pixels on the inner circumferential side in the radial direction where there is a large overlap between exposures.