PURPOSE: To prevent a malfunction, which is unnecessary for replacement of an edged tool, in a driving control system during the replacement of the edged tool.

CONSTITUTION: An operation key switch instructing connection/disconnecting of a feed line to the whole of a work machine and a grinding wheel replacement key switch connecting/disconnecting a feed line to a system required for replacement of a grinding wheel are arranged via an interlock. Normally open contacts MS1a, MS2a, MS4a1, MS3a of a magnet switch, which disconnect a feed line to a system unnecessary for the replacement of the grinding wheel, and a normally close contact MS3b and the like connecting a feed line to a system necessary for the replacement of the grinding wheel when the operation key switch instructs disconnection and the grinding wheel replacement key switch instructs connection are arranged.