PURPOSE: To enable a polishing removal on the spot without getting an annular valve seat out of a piping having a valve or the like and the valve seat by providing a transmission means like an endless belt or the like to transmit a drive force between a thin valve seat polishing disk and a battery driven rotary motor of the disk.

CONSTITUTION: A valve seat polishing disk 1 having a polishing paper 20 adhering thereto is rotated by a motor 2 which is rotated by a cell received in a grip handle 3 through the operation of a switch lever 21. That is, a bevel gear 4 is mounted to a rotary shaft of the motor 2 to mesh with a bevel gear 7 coaxial with a geared belt wheel 6 over which a timing belt 5 as an endless transmitting means to transmit a drive force between the valve seat polishing disk 1 and the motor 2 is trained. The rotation of the timing belt 5 rotates the polishing disk 1 through the geared belt wheel 9 held by a journalling hole in a case 8 consisting of an inner plate 8a and lower plate 8c.