Quasi-electrostatic field on car body surface is considered to be more useful as an in-vehicle communication means, compared with wireless communication and wire harness communication. In this study, we numerically calculated the propagation characteristics on a car body surface for the electric field communication and 2.4 GHz wireless communication, respectively, and showed that the former is more effective to pass through a slit hole in a lower path loss. Moreover, we also expressed the transmitting electrode, the car body and the receiving electrode with an equivalent circuit in view of their near-field coupling characteristic, and yielded the matching impedances of the transmitting and receiving electrodes in order to improve transmission effectiveness.