Abstract: A first guide groove and a second guide groove are formed on a device housing at predetermined positions in such a manner that a first pin disposed at one end of a movable member is displaceably fitted into the first guide groove and a second pin disposed at the other end of the same is displaceably fitted into the second guide groove. To slidably displace the first pin along the first guide groove, a cam is operatively connected to a geared motor. An arm 41 having a frictional member attached to the uppermost end thereof is fixedly secured to the movable member.