A communication system in trains comprises a control data communication device 400 and an image data communication device 300 installed in each of the cars. The control data communication device 400 transmits train operation information, train location information, control instructions of train-mounted apparatuses, and the like. The image data communication device 300 transmits image information such as moving images and still images, audio information such as in-train announcement, textual information for caption display, and operation log information of apparatuses, which form the contents, to a display unit 200 installed in each of the cars and to apparatuses 500 such as a telephone. The display unit 200 switches the display on the screen in accordance with train control information transmitted from the control data communication device 400 through the image data communication device 300.