To eliminate an inconvenience when a stencil base sheet is mounted by preventing the deformation of a clamping plate when opened or closed in a stencil printer for fixing the sheet by the plate.

A rotational shaft 24 is provided in parallel with a central axis on the outer peripheral surface of the peripheral wall of a plate cylinder 4. A clamping plate 7 is openably and closably mounted at the shaft. The position of the plate is sensed by a plurality of magnetic sensors 32. The plate is opened and closed by opening/closing means detachably coupled to the shaft 24. When a stencil base sheet 8 is sent from an engraving unit, the plate at the open or closed position is set to a semi-open position as shown. Thereafter, the opening/closing means is drawn from the shaft 24. The plate becomes free, and is tilted down to the closed position by its own weight. The front end of the sheet is sandwiched between the plate and a plate seat 24 and held. The plate is not deformed, and the front end of the sheet can be once fixed along its width direction. The sheet is not deviated.