To provide a diesel engine start system and a diesel engine start method smoothly starting a diesel engine with solo vegetable oil even if ambient temperature is low, below 5C for example.

A system 10 starting a diesel engine by using vegetable oil even under very cold environment, is provided with a diesel engine 1, a means 20 providing the diesel engine 1 with fuel of which viscosity is dropped by heaters H1-H4, and a means 2 injecting liquefied gas 231 to an intake manifold 8.