A magnet strip extends along a line on the peripheral surface of a printing drum of a rotary stencil printing device and parallel to the rotational axis thereof. A clamp strip, made of a material which is magnetically attractable, can be selectively positioned as lying against and along the magnet strip with a leading edge of a stencil master for stencil printing interposed therebetween so as to clamp the leading edge of the stencil master to the printing drum, or removed away from the magnet strip so as to release the stencil master. Thereby the stencil master can be conveniently retained to the printing drum in a manner which is suitable for automation, and does not require any reinforced lug portion along the leading edge of the stencil master.