An optical device includes a light guiding member that guides light an optical element that functions by being irradiated with the light guided by the light guiding member and a holding member that internally includes a first housing portion housing the light guiding member and a second housing portion housing the optical element and internally holds the light guiding member and the optical element by the first housing portion and the second housing portion so that the light guiding member and the optical element are internally coupled optically. The first housing portion and the second housing portion are communicatively connected inside the holding member and the light guiding member housed in the first housing portion and the optical element housed in the second housing portion are in contact with each other inside the holding member.