plate 21 and the rear end of projecting ridge 37 are disengaged from each other and plate 21 is returned to the initial position in contact with stopper 24 by the biasing force of spring 23 at this time abutting portion 34 of plate 21 pushes the medium in the unloading direction and ejects the medium then the distal end portion of plate 21 is located under plate 16 again so as to prohibit the downward pivoting of plate 16 in this medium unloaded state even if lever 1 is pivoted downward through about 90 u00b0 to perform clamping since the distal end portion of plate 21 is located under plate 16 to prohibit its downward pivot as described above opener 17 is not moved downward therefore s1 head 12 is not moved downward thereby preventing direct contact between heads 12 and 13 in this case arm 20 is pushed down by the distal end portion of clamper pressure plate 4 since arm 20 is made of a leaf spring it is elastically bent thereby preventing overloading of the respective components of the mechanisms fig8 shows a second embodiment of the present invention in the second embodiment paddle stopper arm 50 is provided in the vicinity of the end portion of plate 16 arm 50 is supported by pin 51 so as to be pivotal in a horizontal plane and is biased by coil spring 52 so as to pivot counterclockwise inclined abutting portion 53 is formed on one end portion of arm 50 the side portion of medium 54 loaded in the direction of arrow a is abutted against portion 53 and pivots.