A detection device includes: a detection member that includes an emission member emitting a beam toward a transportation direction of a transportation path and a beam receiving member receiving a reflected beam of the beam emitted from the emission member, and that detects an image on a medium; a transmissive member that allows the beam emitted from the emission member and the beam reflected from the medium to be transmitted therethrough; and a support member that has an open portion blocked by the transmissive member, and that supports an upstream end portion of the transmissive member in the transportation direction of the medium at an upstream portion of the open portion toward the medium, an edge portion of a downstream portion of the open portion in the transportation direction being located closer to the emission member than a bottom surface of the transmissive member.