PURPOSE: To permit the pressure relief for the pressure left in a fuel pipe by the simple operation after the stop of a fuel pump and improve workability by securing the safety when the necessity of demounting a fuel pipe is generated in the trouble diagnosis or the periodical inspection.

CONSTITUTION: When a fuel pump is in stop, a specific instruction is inputted to judge if a fuel pressure relief demand exists or not (S201, S202), and if the fuel pressure relief demand exists, an injector is opened (S203). It is judged if a set time TST lapses or not from the opening of the injector (S204), and if the set time TST lapses, the injector is closed (S205). Accordingly, even in the case where the necessity of replacing a fuel filter in periodical time or demounting a fuel pipe in order to check the fuel pressure in the inspection of the trouble of a fuel injection system is generated, the pressure in the fuel pipe can be lowered to the pressure level free from the generation of the fuel blow-out by the simple operation, and safety is secured, and workability can be improved.