A magnetic resonance isolator includes a ferrite member, a junction conductor that is arranged on the ferrite member and that includes a first port, a second port, and a third port, a permanent magnet that applies a direct current magnetic field to the ferrite member, a capacitor as a reactance element, and a mounting substrate. A main line arranged between the first port and the second port does not resonate, and an end of a sub-line branching from the main line defines the third port. The capacitor is connected to the third port and to the ground. The phase of a wave reflected from the sub-line is adjusted so as to be shifted by about 90 degrees at the intersection of the junction conductor.