Abstract: An optical device for implementing passive alignment of parts and a method therefore, more particularly an optical device and a method therefore that utilize an alignment reference part 115 arranged on the substrate 110 to passively align an optical element part 111 with a lens-optical fiber connection part 120. For the passive alignment of parts, connection pillars 115b of an alignment reference part 115 are coupled to substrate holes 114, one or more light-emitting elements 111a and one or more light-receiving elements 111b are aligned in a row in a particular interval with respect to alignment holes 115a arranged opposite each other in the alignment reference part 115, a lens-optical fiber connection part 120 is aligned with respect to the alignment holes 115a, and an optical fiber 133 is aligned with the optical alignment point at a surface 122b of a prism forming a portion of the lens-optical fiber connection part 120.