PURPOSE: To prevent a roller surface from damage in the burst of a tube by enclosing liquid in a case and operating a control section to stop the drive of a concrete pump when pressure in the case becomes high.

CONSTITUTION: When a tube is burst, concrete in the tube flows into liquid in a case 1 to provide high pressure due to heavy pressure of the concrete in a conduit. Since this liquid pressure presses a piston 16 against a force of a spring 17, a contact 18 contacts a contact 19 by a press piece 20. Thus, current is supplied to a solenoid to change over a controlling valve to the left position and stop the drive of a hydraulic motor 2 without giving any damage of roller surface.