A disclosed paper supply unit includes a paper supply cassette having a bottom plate for placing stacked recording media therein and a sending out part. When the paper supply cassette is loaded at a paper supply position, the sending out part faces the bottom plate, the bottom plate is lifted and the recording media come into contact with the sending out part. A support member is rotatably fitted to the paper supply cassette. An elastic member is fastened between the support member and the bottom plate. The support member has plural fastening parts for fastening the elastic member. The elastic force of the elastic member is changeable by using the plural fastening parts. The invention also discloses an image forming apparatus comprising the paper supply unit.