To provide a compact medium support device including a set tray of a medium detachably arranged in a fixing attachment using a positioning pin and including a lever which is turned in a direction intersecting with a direction of detaching the set tray to move the fixing attachment in the detaching direction.

A medium support device includes: a set tray 4 including a positioning projection section 10 formed on the side opposite a setting surface of a medium; a fixing attachment 9 having the set tray 4 detachably arranged on a disposing surface and including a through-hole which is fitted to the projection section 10 and passes through in detaching directions D1 and D2 on the disposing surface; and a lever 11 that is turned in directions C1 and C2 intersecting with the detaching directions D1 and D2 to move the fixing attachment 9 in the detaching directions D1 and D2. The projection section 10 projects from the fixing attachment 9 through the through-hole when the set tray 4 is disposed in the fixing attachment 9. A rotation range R2 of the lever 11 includes an allowable area R1 where the projection section 10 can exist, projecting from the fixing attachment 9. The projection section 10 projecting from the fixing attachment 9 retreats in the detaching direction D1 from the rotation range R2 of the lever 11 when the lever 11 is turned in the allowable area R1.