The present invention relates to a one-touch chamfering-amount adjustment device for a chamfering machine which specifically carries out a chamfering process on the welding bead surfaces of objects to be processed (such as metal sheet materials and pipes). In the present invention, the moment after a chamfering-amount-adjustment piece has been manipulated so as to rotate, a position-setting pin is inserted into a securing recess in the chamfering-amount-adjustment piece and as this happens the chamfering amount is precisely adjusted in units and at the same time locking to the predetermined chamfering amount is automatically maintained, yet nevertheless the adjustment of the chamfering amount is achieved in a straightforward fashion with one touch, and, when the chamfering-amount-adjustment piece is manipulated, a cutter shaft moves vertically and as it does so the chamfering amount is adjusted in such a way that the chamfering amount can be immediately and rapidly adjusted even during working regardless of any cutter rotating action.