To provide a machining device for a plate object to be polished without dispersion in processing and that is miniaturized with higher economy and high reliability.

This machining device for a plate object to be polished consists of crystal vibration chips B, a polish block 1 to which a plurality of container sections 11 are formed to contain media, and a cover 2 that covers a plurality of the container sections. Side walls 111, 112, 113, 114 in the inside of each container section are linearly tapered so that the area formed by the sidewalls 111, 112, 113, 114 is gradually narrowed, one crystal vibration chip and each medium are contained in each container section of the polish block. An ultrasonic wave generator is locked to the polish block while the cover is placed on the upper face of the polish block and generates an ultrasonic wave to the polish block to polish the plate objects to be polished.