A method for manufacturing an optical element in which a display quality of a projection image is improved is provided. The method is for manufacturing an optical element having a polarization plate of which one side a transmissive member is bonded. The method includes preparing a light source, a polarization plate, a transmissive member, a certificating polarization plate and a spectrophotometer; arranging the polarization plate, the transmissive member, and the certificating polarization plate between the light source and the spectrophotometer; measuring a light transmittance spectrum of a predetermined wavelength at each rotational position of the transmissive member; determining the rotational position of the transmissive member that yields a smallest value for a difference between a maximum value and a minim value of the light transmittance spectrum; and bonding the transmissive member to the polarization plate at the determined rotational position.