An optical scanner provided with at least one optical path through which an optical beam emitted from a light source is directed onto a surface of an object for forming an image thereon includes a deflector configured to deflect the optical beam and a curvature adjustment unit. The curvature adjustment unit includes a reflecting mirror configured to reflect the optical beam in a predetermined direction, a holder unit configured to hold the reflecting mirror and including at least one supporter that engages the reflecting mirror, a pressure unit configured to flexibly deform the reflecting mirror in a normal direction relative to a reflecting surface of the reflecting mirror, and a fixing member fixed to at least a portion of the reflecting mirror, configured to fix a position of the holder unit relative to the reflecting mirror in a main scanning direction by contacting at least a portion of the holder unit including the supporter.