A paper supply mechanism comprising a roll paper compartment for storing roll paper, a first side wall that can move and defines one side of the roll paper compartment, a second side wall that defines the other side of the roll paper compartment, a lock mechanism that locks the first side wall, a roll paper urging member that urges the roll paper in a storage width direction of the roll paper compartment; and a holding mechanism that operates in conjunction with the lock mechanism and holds the roll paper urging member in a predetermined position.