A radio transmission apparatus for TV game machine, a radio transmission adaptor connectable to a main body of existing TV game machine, and a TV game cassette provided with a radio transmitting antennae are disclosed as radio transmission system for TV game machine. According to the radio transmission system, radio frequency output signals representing game data contained in TV game cassette is amplified and transmitted by radio to feeder or indoor antennae connected to TV set having no special receiving portion to receive the transmitted game data, thereby attaining wireless transmission of game data.