Disclosed is a spark-ignition gasoline engine, which comprises control means operable, when an engine operation zone is a high-load operation zone including a WOT region within at least a low speed range, to adjust a closing timing of an intake valve in such a manner as to maintain an effective compression ratio at 13 or more, and retard an ignition timing to a point within a predetermined stroke range just after a top dead center of a compression stroke, wherein the effective compression ratio is calculated based on an intake-valve closing timing defined by a valve lift amount of 1 mm. The present invention can provide a spark-ignition gasoline engine having both a low-cost performance and a high engine-power performance even in a high-load operation zone (particularly WOT region) in a low speed range.