Provide are an imaging device and an optical transmission module that are reduced in size and allow high-speed signal transmission between a signal processing device and an image sensor having a large number of pixels. An optical transmission module according to the invention includes: a photoelectric conversion element that converts an electrical signal to an optical signal; a photoelectric conversion element-driving IC that drives the photoelectric conversion element; an optical fiber that transmits the optical signal emitted from the photoelectric conversion element; a guide holding member that guides and holds the optical fiber; a cable that supplies power to the electronic component; and a substrate on which the electronic component is mounted. The substrate has at least a first plane and a second plane. The first plane and the second plane are perpendicular to each other. The photoelectric conversion element is mounted on the first plane. The optical fiber is connected to a back side of the first plane through the guide holding member such that an optical axis of the optical fiber is perpendicular to the first plane. The cable is connected to the second plane in parallel with the optical axis of the optical fiber.