To heat a steel sheet to temperatures which are partially different by a single heat treatment when heating the steel sheet to the temperatures which are different partially.

The blank material is heated at the same time by a single heat treatment to partially different temperatures according to the heating temperatures of a plurality of heating regions 20a, 20b, ..., of the heating surface with a hot plate 12 which has a flat heating surface (top surface 12f) to be brought into close contact with the blank material, and whose heating surface is divided into the plurality of heating regions 20a, 20b, ..., with a lot of sheathed heaters 18a-18m to be heated to different heating temperatures. In this way, when heating the blank material to partially different temperatures for partially quenching and hardening the blank material such as a reinforcing member for a center pillar, for example, the heat treatment can be easily performed in a short period of time, and temperature control is easy since the heating is performed at a time, and objective temperature distribution is obtained with high precision.