A high frequency transformer with high conversion efficiency is provided. The high frequency transformer includes a first coil assembly 1 formed from a single flat wire, with first coils 1A that are configured by winding the flat wire edgewise plural times and that are formed at specific intervals, and a second coil assembly 2 formed from a single flat wire, with second coils 2A that are configured by winding the flat wire edgewise plural times and that are formed at specific intervals. In the primary coil assembly 1 and the secondary coil assembly 2, the primary coils 1A are disposed at intervals to each other such that a winding end portion of one of adjacent primary coils 1A opposes a winding start portion of the other of the adjacent primary coils 1A, and one of the secondary coils 2A is disposed in each interval between the primary coils 1A such that a winding start portion of each secondary coil 2A opposes the winding end portion of one of the primary coils 1A, and a winding end portion of each secondary coil 2A opposes the winding start portion of the other of the primary coils.