A sheet cassette includes a cassette main body which forms a sheet accommodating region; an edge guide which is slidable to a position corresponding to a size of a medium; a guide groove which extends along a sliding direction of the edge guide and guides the edge guide in the sliding direction, and into which a portion of the edge guide is inserted; and a widening allowance groove which is provided with a predetermined distance from the guide groove, and allows widening of the guide groove when a portion of the edge guide is inserted into the guide groove.