The present invention has been made in view of the above-mentioned problems, and is intended to carry out ignition to a mixture in a more stable manner in a multi-fuel internal combustion engine. In the control apparatus for a multi-fuel internal combustion engine which is able to be operated by mixed combustion of a plurality of kinds of fuels, a mixing ratio of the plurality of kinds of fuels is controlled by a mixing ratio control unit, and ignition timing of a spark plug is controlled by an ignition timing control unit, in such manner that a required discharge voltage is made equal to or less than a voltage which is lower by a fixed value than a voltage to be applied to said spark plug (S104, S108).