To make a hole in a sheet with a small shift from a predetermined punching position even if the sheet is skewing.

The punching device includes: a punching part 220 for making a hole in a sheet: side edge detection sensors S2 and S3 that can move with the punching part in an integrated fashion in a direction that intersects with a sheet conveying direction and detects a side edge of the sheet along the sheet conveying direction; a pinion 211 and a rack 221 that move the punching part and the side edge detection sensors in an integrated fashion in a direction that intersects with the sheet conveying direction and cause the side edge detection sensors to detect the side edge of the sheet; and a control device for controlling the punching part, and the pinion and the rack. The control device causes the pinion and the rack to move the punching part and the side edge detection sensors. When the side edge detection sensors detect the side edge of the sheet, the control device stops the movement of the punching part and the side edge detection sensors by the pinion and the rack, and causes the punching part to conduct punching operation.