A denting device for forming a predetermined pattern on a surface near a discharge hole and an intake hole of a valve plate for a compressor includes: a seating jig to which the valve plate is fixed; a processing pin in which a pressing part for pressing the valve plate is formed at a distal end thereof; and a moving unit which is disposed on an upper portion of the seating jig, horizontally moves the processing pin at a constant speed while allowing the processing pin to vertically reciprocate at a constant speed, so as to form the pattern on the valve plate.