Both thickened end portions of predetermined lengths of an upset steel pipe are preheated simultaneously, in advance of heat treatment of the pipe, in an apparatus provided with means for raising or lowering the stationarily supported upset steel pipe and with a pair of induction heaters for simultaneously heating both end portions of the upset steel pipe in the raised position of the pipe, said pair of induction heaters being set in advance to a relative spacing corresponding to the length of said steel pipe, and reciprocated with strokes corresponding to the lengths of the thickened end portions. The support means for raising and lowering the pipe comprise a plurality of units which may be raised and lowered separately and selectively.