An optical device is described that include: a photoemitter for emitting light, a mounting unit for installing a transparent container accommodating a sample to be subjected to detection, a photoreceptor for receiving the light emitted by a photoemitter and transmitted through the transparent container installed in the mounting unit, a first member disposed between the transparent container and the photoreceptor and having a first pinhole through which passes the light transmitted through the transparent container, and a second member disposed between the first member and the photoreceptor and having a second pinhole through which passes the transmitted light that has passed through the first pinhole.