An engine controller is applied to a system that includes an engine and an exhaust purifying catalyst for purifying exhaust gas of the engine. The engine controller has an idle stopping means, a catalyst temperature detecting means and an engine restarting means. The idle stopping means stops the engine when a predetermined idle stop condition is satisfied. The catalyst temperature detecting means detects a temperature of the exhaust purifying catalyst while the engine is stopped by the idle stopping means. The engine restarting means restarts the engine when the temperature of the exhaust purifying catalyst, which is detected by the catalyst temperature detecting means, becomes equal to or lower than an engine restart determination temperature, which is determined on a basis of an activation temperature of the exhaust purifying catalyst.