PURPOSE: To align an optical axis to axial centers of components easily with high precision and to obtain the low-cost, high-performance optical device by inserting and adhering an optical fiber in a guide groove formed of a couple of guide elements.

CONSTITUTION: The couple of guide elements 14 and 16 are provided on the surface of a quartz substrate 10 successively in series while facing each other across guide grooves 14a and 16a, and an element glass substrate 15 is provided slantingly by 45° to the prolongation of te guide groove 14a. Further, a couple of guide elements 17 are provided forming a guide groove 17a at right angles to the prolongation of the guide groove 14a. Then, surfaces of the element glass substrate 15 are masked except the vertical surface at the side of the guide element 14 and a desired dielectric multi-layered film is vapor-deposited on this vertical surface to form a filter film 20. Terminal parts of an incidence optical fiber 5A and projection optical fibers 5B and 5C are inserted into the guide grooves 14a, and 16a and 17a and fixed by charging an adhesive. This obtained optical device has high size precision of the guide grooves and high precision of relational size, so optical axes are easily aligned to axial centers only by inserting the optical fibers.