A post-processing device includes an introductory conveying path, a processing tray, a paper receiving tray, an upper paper discharge roller, a lower paper discharge roller and a control section. The upper paper discharge roller and the lower paper discharge roller are disposed at an edge portion on the paper receiving tray's side of the processing tray. The upper paper discharge roller is capable of coming into contact with and away from the lower paper discharge roller. The control section causes the upper paper discharge roller to start a descending motion with a timing such that the upper paper discharge roller comes into contact with paper before the paper comes into contact with the paper receiving tray if the paper belongs to a second kind, where the paper of the second kind is lighter weight than that of a first kind.