This invention has building members which include an image sensing portion, an optical member for forming a beam from an object to be sensed into an image on the image sensing portion, a positioning portion which positions the optical member, and a support member which holds the optical member and to which the positioning portion is fixed. When the optical member deforms along the optical axis upon a temperature change of the building members, the image sensing portion is deformed in the same direction as deformation of the optical member. The position of the image sensing portion is adjusted via a plurality of adjustment members movably attached to the support member. The image sensing portion is fixed to the support member after adjustment by adhering the image sensing portion and the adjustment members to each other, and adhering the adjustment members and the support member to each other.