A stratified internal combustion engine has a trap chamber for rich mixture having suction and discharge apertures communicating the trap chamber with the principal combustion chamber. A separating wall is provided between the suction and discharge apertures to divide a portion of the trap chamber into two spaces or pockets, one communicating with the suction aperture and the other communicating with the discharge aperture, for thereby facilitating the introduction of rich mixture into the trap chamber and scavenging the residual gases in the trap chamber and improving the trapping effect of the trap chamber with a resultant improvement in stratified combustion in the engine.