To provide a reaction force device which facilitates reaction force adjustment, reduces operation force, and is suitable for multi-stage adjustment, and also to suppress the increase of a manufacturing cost.

The reaction force device for a chair includes: a plurality of rod- or plate-like springs 3 arranged between a base body 1 and a rocking body 2 connected to the base body 1; actuation changeover cams 6 arranged in each spring 3 so as to be rotatable and displacable between a projection position 4, where cam surfaces 6b abut on the corresponding springs 3, and a retreating position 5, where the cam surfaces 6b are positioned further from the corresponding springs 3 compared with the projection position 4; and an operation device 7 for rotating and displacing the actuation changeover cams 6. The outer peripheral surface is defined as the cam surface 6b in each actuation changeover cam 6. The operation device 7 includes a plurality of reaction force adjustment positions which are different in combinations between the actuation changeover cams 6 to be displaced to the projection position 4 and the actuation changeover cams 6 to be displaced to the retreating position 5. The actuation changeover cam 6 displaced to the projection position 4 bends the corresponding spring 3 in response to the rocking of the rocking body 2, so as to generate the reaction force with respect to the rocking.

COPYRIGHT: (C)2009,JPO&INPIT