A sheet supply device comprising: a lift portion that lifts and inverts a sheet group including aplurality of flatly stacked sheets; a conveyor portion that moves each sheet of the sheet group transferred from the lift portion in a transport direction; wherein the lift portion includes a frame that extends in a flat stacking direction of the sheet group, a fork portion that is supported by the frame so as to be movable in the flat stacking direction and has the sheet group mounted thereon, an inversion mechanism that turns the fork portion to lift and invert the mounted sheet group, and a fork movement mechanism that moves the fork portion in the flat stacking direction, characterized in that the sheet supply device further comprises: a width-direction movement mechanism (60,61,62,63,64) that is equipped on the lift portion and moves the mounted sheet group in a width direction; a position sensor (70,71,72,73) that detects a width-direction position of the sheet group; and a centering control device that controls the width-direction movement mechanism (60,61,62,63,64) on the basis of detection information of the position sensor (70,71,72,73), and centers the width-direction position of the sheet group within a reference width-direction range, from when the sheet group is mounted on the fork portion to when the sheet group is transferred to the conveyor portion. a lift portion that lifts and inverts a sheet group including aplurality of flatly stacked sheets; a conveyor portion that moves each sheet of the sheet group transferred from the lift portion in a transport direction; wherein the lift portion includes a frame that extends in a flat stacking direction of the sheet group, a fork portion that is supported by the frame so as to be movable in the flat stacking direction and has the sheet group mounted thereon, an inversion mechanism that turns the fork portion to lift and invert the mounted sheet group, and a fork movement mechanism that moves the fork portion in the flat stacking direction, characterized in that the sheet supply device further comprises: a width-direction movement mechanism (60,61,62,63,64) that is equipped on the lift portion and moves the mounted sheet group in a width direction; a position sensor (70,71,72,73) that detects a width-direction position of the sheet group; and a centering control device that controls the width-direction movement mechanism (60,61,62,63,64) on the basis of detection information of the position sensor (70,71,72,73), and centers the width-direction position of the sheet group within a reference width-direction range, from when the sheet group is mounted on the fork portion to when the sheet group is transferred to the conveyor portion. a width-direction movement mechanism (60,61,62,63,64) that is equipped on the lift portion and moves the mounted sheet group in a width direction; a position sensor (70,71,72,73) that detects a width-direction position of the sheet group; and a centering control device that controls the width-direction movement mechanism (60,61,62,63,64) on the basis of detection information of the position sensor (70,71,72,73), and centers the width-direction position of the sheet group within a reference width-direction range, from when the sheet group is mounted on the fork portion to when the sheet group is transferred to the conveyor portion.