To provide a working machine for printed circuit board capable of improving working accuracy and efficiency.

A plurality of cylinder parts 21 are formed in a holder 20 to hold piston members 30 movably in the axis line direction. Back pressure chambers 35 are formed between the cylinder parts 21 and the back face side of the piston members 30 so that these back pressure chambers communicate with each other via communication flow paths 23 and the back pressure chambers 35 and the communication flow paths 23 are filled with oil 40. Even when the surface of the printed circuit board W is inclined, since each pressing part 33 certainly presses the surface of the printed circuit board W, the printed circuit board W is prevented from moving undesirably when drilled by a drill 13.