Engine automatic-stop/restart system and engine automatic-stop/restart method

An engine automatic-stop/restart system that stops fuel injection into an engine so as to stop the engine when an engine automatic stopping condition is satisfied and then restarts the engine when an engine restarting condition is satisfied, the engine automatic-stop/restart system comprising:

• a crank angle sensor that outputs a crank pulse signal in accordance with a crank angle of a crankshaft of the engine;
• a starting apparatus that cranks the crankshaft so as to restart the engine;
• a starting apparatus drive start waiting time calculation unit that calculates, while the engine is inertially rotating, a starting apparatus drive start waiting time in which an engine rotation speed becomes the same as or lower than a predetermined threshold value, based on a gradient of a change in the engine rotation speed and the engine rotation speed detected on the basis of an output of the crank angle sensor;
• and
• a starting apparatus drive start setting unit that sets in an output comparison register provided in an microcomputer a starting apparatus drive starting time instant obtained by adding the calculated starting apparatus drive start waiting time to a present time instant read from a free-running counter provided in the microcomputer and that starts drive of the starting apparatus by use of an output comparison register function, of the microcomputer, that generates an output when the set starting apparatus drive starting time instant and the value of the free-running counter coincide with each other.