To provide a pressure relief device for automatically or manually relieving a pressure when a high pressure grout pump exceeds a predetermined pressure.

A pressure relief device is configured to relieve a pressure when a grout pump exceeds a predetermined pressure, and includes at least: a block element 14 including a cylinder part 12 communicating with a pressure relief passage 19 and a discharge hole 13; a valve member 15 which is shaped tubular, has a tapered portion in the middle, includes a packing part 15d in the end portion thereof and is disposed in the cylinder part 12; a safety pin 16 which is inserted into the valve member 15 and includes at both end portion sides missing part which are broken when receiving a predetermined pressure; a push-in bolt 17 of which one end portion 17a can push in the valve member 15 and the other end portion 17b is positioned while protruding from an upper portion of the block element 14. Both end portions (a) of the safety pin 16 are held between a lower portion of the block element 14 and an edge 23 of the pressure relief passage 19, and the valve member 15 is fixed temporarily.