To provide an intra-cylinder fuel injection engine and a piston for it, whereby it is possible to establish stratification even if a wide atomization angle with good performance to turn into particulates is used, ensure good transporting characteristics to an ignition plug, generate satisfactory mixing with the air, and suppress generation of smokes and hydrocarbons.

This intra-cylinder fuel injection engine is structured so that the fuel is injected directly into a combustion chamber from a fuel injection device 31 and combusted, and a piston 23 used in the engine is configured so that a cavity 39 as a recess in an egg form when viewed on the plan is formed at the top 36 and that the thinner tip 39a of the egg form of this cavity 39 is positioned in the central part of the top face of the piston while the thicker base end 39b of the egg form is located near the injection port of the fuel injection device 31, and thereby the fuel is injected from the base end 39b toward the thinner tip 39a.