17 is zero the velociy v of the patter assembly 6 is therefore zero from the equation 1 in this state the actuator 4 is moved to the extreme right side the relative position of the patter body 9 and the patter slide tube 10 slidably fitted to the patter body 9 is such that the flange 10b of the patter slide tube 10 is located at the farthermost position from the plate member 7 as shown in fig8 as the rotating disc 17 rotates from the state shown in fig2 to the state shown in fig3 or as the cushion member 8 of the patter assembly 6 becomes flush with the open end face of the space guide 5 the patter assembly 6 is moved at the velocity v given by the equation 1 that is the cushion member 8 of the patter assembly 6 strikes the skin surface at the velocity v so long as the skin surface being treated exists at the open end face of the space guide 5 until this moment the relative position of the patter body 9 and the patter slide tube 10 remains essentially unchanged from the state shown in fig2 fig4 shows the state where the rotating disc 17 further rotates until the rotating angle u03b8 becomes u03c0 with no.