Fuel gas supply and purge system for diesel engine

The purpose of the present invention is to enable switching from fuel-gas operation to fuel-oil operation, without temporarily stopping a diesel engine in cases when, during fuel-gas operation in which a fuel gas is injected from gas injection valves, a gas injection valve fails while open and cannot close, and inert gas is to be used to purge the fuel gas that has accumulated in an accumulator, when switching from fuel-gas operation in which the fuel gas is injected from the gas injection valves, to fuel-oil operation in which a fuel oil is injected from fuel-oil injection valves. Accordingly, valves (82) set in a fully closed state when switching from fuel-gas operation to fuel-oil operation are provided to midpoints of fuel-gas supply pipes (66) which guide, to gas injection valves (61) provided so as to correspond to respective cylinders of a diesel engine, a fuel gas which has been guided from a fuel-gas supply source, and which has accumulated inside accumulators (65) provided so as to correspond to the respective cylinders of the diesel engine.