A velocity detecting device includes an image-pattern acquiring unit that includes a laser light source and an area sensor that acquires a one-dimensional or a two-dimensional image. The image-pattern acquiring unit includes a lens between a moving member and the area sensor, irradiates a beam emitted from the laser light source to the moving member to make a scattering light of the moving member scattered from the moving member on the area sensor by using the lens, and acquires an image pattern at a predetermined time interval in association with movement of the moving member. A velocity calculating unit calculates the velocity of the moving member by computing the image pattern acquired by the image-pattern acquiring unit. The lens is a reduced optical system that projects a reduced object onto the area sensor.