A portable audio player (100) includes a decoder (14) and other devices for reproducing audio data, a microcomputer (16) for controlling starting and stopping the reproduction, and a radio communication device (24). An on-vehicle audio player (200) includes a radio communication device (64) for a bidirectional radio communication with the radio communication device in the portable audio player, a decoder (54) and other devices for reproducing audio data, and a microcomputer (56) for controlling starting and stopping the reproduction. In case that the portable audio player stops reproducing the audio data, the on-vehicle audio player starts reproducing the audio data.