To improve the buffering device of a chart disk supporting body, and to attain assembling by mass production by providing a pressure accumulator, connecting this pressure accumulator with a chart disk supporting body, and correspondingly arranging a stopper fixedly positioned at the pressure accumulator at a pivotally supporting position.

A catch arm 40 is integrally formed at a joint rail 16, and the catch arm 40 is allowed to function as a stopper for a lever 28 at an inserting/pulling-out position. Only an added part 41 formed at the catch arm 40 and a leg spring 42 supported on a shaft 14 are provided as a buffering device. One leg part 43 of the leg spring 42 is held in an opening 44 formed at a chart disk supporting body 6, and the other leg part 45 of the leg spring 42 is action-connected with the added part 41 formed at the catch arm 40 during the rotation of the chart disk supporting body 6. Also, a restraining body 46 having a protruding part 47 can be elastically deformed into a prescribed form.