To provide a heat treatment method for homogenizing the whole steel sheet, by reducing the non-steady part generating at a head part and a tail part of the steel sheet when heating it with an induction heating device, and an apparatus therefor.

This apparatus includes arranging several induction heating devices 5-1 to 5-6 at intervals, and conveyance roller groups 8a, 8b, and 8c, each having an independently variable conveyance speed, for passing a steel sheet 1 through the induction heating devices. This method includes sequentially heating them, while approaching the rear end of the precedent sheet 1-1 to the top end of the following sheet 1-2. The method alternatively includes sequentially heating them, while arranging a dummy material 14 ahead of the precedent steel sheet 1-1 and/or behind the following steel sheet 1-2, so that they can come close.