Two coil conductors of the same spiral shape are cut out from a lead frame. The two coil conductors are disposed back to back so that the front of a first coil conductor is superimposed over the rear of a second coil conductor. Central end portions of the first and second coil conductors are connected to each other through a connection layer. Outer end portions of the spirals of the first and second coil conductors are connected to corresponding ones of first and second terminals of the thin inductor, respectively. A sintered green sheet as a magnetic substance is disposed in gaps between the first and second coil conductors. In this manner, the invention can provide a thin inductor small in size, strong in mechanical strength and inexpensive, a method of producing the thin inductor, and an ultra small size power conversion apparatus using the thin inductor.