An in-vehicle communication apparatus includes an antenna module, and a wireless communication device physically separated from the antenna module and connected to the antenna module through a coaxial cable. The antenna module includes an antenna, and a transmission amplifier of the antenna. The wireless communication device includes a power generation portion that supplies a power driving the antenna module, a signal generation portion that generates a transmission signal, a power superimposition portion that superimposes the transmission signal on the power supplied from the power generation portion, and transmits a superimposed power to the transmission amplifier, a current detection portion that detects a consumption current value from the power, a correspondence relationship hold portion that holds a correspondence relationship between the consumption current value and an output power value, and a regulation portion that adjusts the transmission signal to maintain the output power value at a predetermined power value.