An imaging device includes: a holder that has a substantially hollow cylindrical shape having first and second end portions, both of the first and second end portions being opened in a longitudinal direction of the holder, the holder having a cutout portion on a side surface of the first end portion; a lens group provided inside the holder and configured to collect light incident from the second end portion of the holder; an optical member provided inside the holder and configured to transmit or reflect the light collected by the lens group; and an image sensor configured receive the light from the optical member. Part of an outer surface of the optical member is a columnar surface, and the columnar surface of the optical member abuts on an inside of the holder. Part of the image sensor is attached to the side surface of the holder through the cutout portion.