An optical apparatus includes: a housing; at least one component housed in the housing, the at least one component being configured to be energized and perform at least one of outputting light, receiving light, and changing a property of light; a plurality of external connection conductors configured to penetrate through the housing; and a flexible substrate housed in the housing, the flexible substrate including an insulation layer, a plurality of conductive wires each configured to perform at least one of conduction between the component and the external connection conductors, conduction between the external connection conductors, and conduction between a plurality of the components each serving as the at least one component, a base part in which the conductive wires are covered by the insulation layer, and a plurality of arm parts protruding and extending from the base part, each including one of the conductive wires.