A cup attaching apparatus for attaching a cup serving as a machining jig on a surface of a lens comprises: a white LED which is an illumination light source for illuminating the lens placed on a lens supporting member; a screen applied with an alignment mark, on which screen an image of the lens illuminated by illumination light from the white LED is projected; a movement device which moves the cup set in an arm toward the lens along a reference axis for cup attachment, the position of the reference axis being associated with the alignment mark; and a light intensity increasing and decreasing device which increases and decreases light intensity of the white LED in response to an operation signal from an operation member to be operated by an operator, the operation member being placed on a front of a housing of the apparatus.