An internal combustion engine with variable valve opening characteristics includes an outer camshaft, an inner camshaft, an urging device, a cam phase changing device, and a locking device. The outer camshaft includes a first cam. The inner camshaft includes a second cam. The cam phase changing device includes a first rotating member, a second rotating member, an advance-angle-side oil hydraulic chamber, and a retard-angle-side oil hydraulic chamber. A cam phase of the one of the outer camshaft and the inner camshaft is changed by switching between oil hydraulic circuits that communicate with the advance-angle-side oil hydraulic chamber and the retard-angle-side oil hydraulic chamber. The locking device is provided to connect another of the outer camshaft and the inner camshaft to the first rotating member with a predetermined cam phase.