PURPOSE: To enhance the working effectiveness for crushing by inserting molten paraffin and a heater wire in a hole provided in an object to be crushed, putting a pressure plug after solidification of paraffin, re-melting it, and crushing a rockbed etc. with its volume expansion.

CONSTITUTION: A hole 2 is bored in a rockbed 1, and molten paraffin 3 and a heater wire 4 are inserted over the scheduled plane. After solidification of paraffin 4 a crown-shaped pressure plug 5 is put, which is made of shape memory alloy and has a temp. a little lower than the molten paraffin. If then the heater wire is heated, molten paraffin 3 is put in pressure contact with the inner walls of the hole without gaps, and at the same time, the internal pressure of the hole is increased because of liquefication volume expansion, and concrete wall 1 is crushed. When current feed to the heater wire 4 is shut, the paraffin 3 will solidify again, and it is collected and re-used. This shortens the time till crushing and enhances the operating easiness.