A reactor 1α includes one coil 2, a magnetic core 3 to which the coil 2 is arranged, and a case 4 containing an assembly 10 of the coil 2 and the magnetic core 3. The magnetic core 3 includes an inner core portion 31 inserted into the coil 2, and a coupling core portion 32 disposed around the coil 2. The coupling core portion 32 is made of a mixture of magnetic powder and resin. The coil 2 is covered with the coupling core portion 32 and is enclosed within the case 4 in a sealed state. The reactor 1α includes, in an outermost surface region exposed at an opening of the case 4, a magnetic shield layer 5 made of non-magnetic powder, having smaller specific gravity than the magnetic powder and having electrical conductivity, and the resin. A small reactor capable of reducing magnetic flux leaked to the outside is thereby provided. A method of producing a small reactor capable of reducing magnetic flux leaked to the outside is also provided which produces the reactor 1α by filling the case 4 with a mixture of magnetic powder, non-magnetic powder, and resin, producing a state where the non-magnetic powder has floated to the opening side of the case 4 and the magnetic powder has precipitated on the bottom side of the case 4, and hardening the resin.