A hinge unit includes a support member, a mount member and a detachment restricting member. The support member configured to support a document pressor pressing a document to a document placing surface provided on a housing openably/closably with respect to the document placing surface. The mount member linked turnably to the support member and mounted removably to the housing. The detachment restricting member whose one end part is connected to the support member and including an engage movable member forming an engage part at another end. The detachment restricting member restricting the mount member from being detached from the housing in a case where the document pressor is closed, and allowing the mount member to detach from the housing in a case where the document pressor is opened.