PURPOSE: To suppress explosion in a compression process by constraining ionized fuel to the line of magnetic force in an internal combustion engine so as to secure a specified compression ratio and appropriately control explosion start timing in an explosion stroke while heightening explosion force by instantaneously releasing the constraint of ionized-fuel cracked gas by the line of magnetic force.

CONSTITUTION: In an internal combustion engine 1, a permanent magnet 3 is disposed in a recessed part formed at the rear side central part of a cylinder head 2, and a permanent magnet 5 is located in a recessed part formed at the back side central part of the piston head 7 of a piston 4. Both permanent magnets 3, 5 are made face each other with unlike poles without being exposed to a combustion chamber 6. The fluctuating magnetic field is thereby formed in the combustion chamber 6 in association with the reciprocating motion of the piston 4.