An optical sensor is installed in a device, and includes a light-emitting element, and a light-receiving element for receiving light emitted from the light-emitting element and traveling through a space. The optical sensor detects an object present in the space, based on a change of the light impinging upon the object. A first optical waveguide is connected to the light-emitting element so as to be capable of light propagation. The first optical waveguide has a front end portion serving as a light exit portion for exiting light emitted from the light-emitting element. A second optical waveguide is connected to the light-receiving element so as to be capable of light propagation. The second optical waveguide has a front end portion serving as a light entrance portion for receiving light exiting from the light exit portion of the first optical waveguide and traveling through the space.