A wall shape of a cavity consists of an inward protruding portion located at the periphery of an opening, a center portion projecting toward a fuel injector, and a peripheral portion connecting the inward protruding portion and the center portion. The fuel injector and the cavity are configured so that fuel injected from fuel injector directs to the proximity of the border between the inward protruding portion and the peripheral portion. The peripheral portion consists of a first portion located farthermost from the fuel injector, a second portion located between the inward protruding portion and the first portion, and a third portion located between the first portion and the center portion. The radii of arcs of the peripheral portion decrease from the second portion to the first portion and increase from the first portion to the third portion.