PURPOSE: To prevent chattering from being generated in oscillation of a printing unit body in a scanning direction, by a method wherein an oscillating vibrating mechanism for oscillating a printing unit body is constructed in a simple construction with a friction-generating part reduced as much as possible.

CONSTITUTION: The oscillating vibrating mechanism A for reciprocating the printing unit body B in the scanning direction is constituted of a rotary shaft 2 rotated by a motor 1, an eccentric shaft 3, a bearing 4 and an oscillating arm 5. Leaf springs 27, 27a suspended from fixed frames 26, 26a on the main body side are fitted to left and right regions of an oscillating supporting part 11 for the printing unit body B, and the supporting part 11 is oscillated in the scanning direction through flexure of the leaf springs 27, 27a.