An optical device comprising a first substrate in which V-grooves are made, four optical fibers, for example, having a reflective function and fixed in the V-grooves of the first substrate, an optical element bonded, through an adhesive layer, onto the optical path of a reflected light at least generated by the reflective function on the outside of the clad of each optical fiber, and a second substrate for mounting the optical element, wherein the second substrate is disposed such that the mounting surface of the optical element faces the first substrate.