A controller for an internal combustion engine (1). The controller includes a means for automatically stopping the engine (1) when predetermined stopping conditions are satisfied, a means for automatically restarting the engine (1) when predetermined restarting conditions are satisfied, and a main switch (71). The controller invalidates the automatic restarting of the engine (1) and starts the engine (1) in a normal manner if the main switch (71) is arranged at a start position after the engine (1) is automatically stopped but before the predetermined restarting conditions are satisfied.