In the data transmission system according to the present invention, a master apparatus transmits data to a plurality of slave apparatuses during a time block T1-1 and the individual slave apparatuses transmit data for the master apparatus during a time block T1-3. Slave apparatus control signals transmitted by the master apparatus for the individual slave apparatuses are transmitted through a control channel group 31 having time slots that correspond to the individual slave apparatuses, whereas master apparatus control signals for the master apparatus transmitted by the individual slave apparatuses are transmitted through a control channel group 35 having time slots that correspond to the individual slave apparatuses. Consequently, even though the data transmission system is constituted through the point-multipoint connection using a 2-wire metallic transmission line, data do not collide with one another in data transmission between the master apparatus and the plurality of slave apparatuses to achieve efficient data transmission.