A plurality of rods (3) each having a bit (2) at a front end are disposed in parallel to one another so that adjacent bits are displaced to some extent forward and backward, and a striking device (4) operatively connected to each of the rods includes a striking block (5). The striking block includes a single cylinder block (6) having a plurality of cylinder tubes (7), and a striking piston (8) is slidably fitted into each of the cylinder tubes (7). The striking block (5) further includes a change-over valve (9) for changing over between a forward movement and a backward movement of each striking piston. A rear end of each rod (3) is connected through an adapter (15) to a shank rod which is connected to the striking device. In the striking device, a spring is provided between a bearing holder (80) which holds the shank rod rotatably and the adapter to push the rod in a forward direction. When the bit is in a postion where it has not reached the rock, the rod is pushed forward by the spring to hold the shank rod at a position before the striking point.
展开▼
