The present invention provides a fixed focus-type photographing apparatus, which can inexpensively and simply increase a depth of field by disposing a removable light diffusion plate in an existing lens optical system, and an optical system of the photographing apparatus. A photographing apparatus includes: an optical system, including two or more than two lenses, a diaphragm disposed between any two adjacent lenses of the lenses, and a light diffusion plate disposed at a position that is in front of a forefront first lens; and a photographing element, disposed at a position that is behind a rearmost final lens, where: the light diffusion plate includes a light diffusion surface, and a distance a from a front surface of the first lens to the diaphragm is less than a distance b from the diaphragm to the photographing element.