A high-frequency transformer includes a primary coil and a secondary coil coupled to each other by magnetic field coupling and sharing a coil winding axis, a first terminal connected to a first end of the primary coil, a second terminal connected to a first end of the secondary coil, and a common terminal connected to a second end of the primary coil and a second end of the secondary coil. The primary and secondary coils are helical coils including loop conductor patterns, and the number of turns of a first loop conductor pattern closest to the second end of the primary coil is larger than an average number of turns of other loop conductor patterns included in the primary coil.