PURPOSE: To scatter the fuel jet stream after collision against a collision face in the space on a swirl chamber and prevent a glow plug and fuel injection valve from interfering with an intake & exhaust valve and its driving part.

CONSTITUTION: A swirl chamber 1, which turns air flow in the direction of the outside of a cylinder more than the direction of a communication passage 3, is formed in the direction of the outside of the cylinder, and the fuel injection direction is faced diagonally to the internal face of the hot plug 4 adjacent to the communication port on the side of the swirl chamber in the wall face downstream of a swirl, and a corner section 6 having an acute angle is projectedly provided between the end section 5b of a collision face and the internal face of the communication passage 3 adjacent to the end section 5b, and a glow plug is inserted into the swirl chamber 1 from the wall face on the non-cylinder side of the swirl chamber 1. Then, a fuel injection valve 7 and the glow plug 8 can be separated from an intake & exhaust valve and its driving part, and fuel jet stream is heated by the glow plug 8 during or after collision so that it can easily ignited.