To suppress exudation of thermosetting resin from the inner layer side of a fiber reinforced plastic layer to the outer layer side thereof when thermosetting the thermosetting resin in a pressure container having the fiber reinforced plastic layer containing a conductive fiber and the thermosetting resin by electromagnetic induction heating.

The thermosetting of the thermosetting resin is performed at a relatively low temperature rising speed while keeping the lowest viscosity of the thermosetting resin relatively higher and subsequently rapidly performed at a relatively high temperature rising speed.