This specification discloses an excellent communication device of a field coupling type that increases field coupling efficiency between electrodes and realizes a small-sized device. This specification also discloses a communication system and an electrode. A communication device 100 includes: a first resonant circuit 121 connected in series to an electrode unit 110 formed with two conductor plates; and a second resonant circuit 122 connected in parallel to the electrode unit 110 and the first resonant circuit 121, which are connected in series. The constant of a resonant circuit is determined so that the voltage V2 to be applied to the electrode unit 110 becomes higher than the voltage V1 to be applied to the electrode unit 110 and the first resonant circuit 121 connected in series. In this manner, a field coupling electrode that has a very high coupling strength at a target frequency is obtained.