Electromagnetic coupling between a pan or utensil load to be heated by magnetic induction and a source of high frequency magnetic flux is sensed by detecting a current which is indicative of the electromagnetic coupling by means of a current transformer. The detected current is compared with a reference level. Intermittent generation of the magnetic flux is commenced when, for example, a small magnetic metal object is inadvertently placed as a load with the result that the detected current becomes lower than the reference level. This allows intermittent check for the presence and absence of the inadvertently placed load for subsequent cooking operations and minimization of the heat generated therein.