An optical device including a contact part having a contact surface and an opposing surface, the contact surface coming into contact with a test subject and the opposing surface being opposite the contact surface a support body installed on the opposing surface a first element supported by the support body and a second element disposed between the opposing surface and the support body wherein one of the first element and the second element is a light-emitting element for emitting light towards a detection site of the test subject another of the first element and the second element is a light-receiving element for receiving reflected light, the reflected light being light emitted by the light-emitting element and reflected at the detection site and the contact part is formed from a material that is transparent with respect to a wavelength of the light emitted by the light-emitting element.
