Disclosed are a device and a method for providing simultaneous data transmission service based on heterogeneous networks. A transmission device of system for simultaneous data transmission service system is configured to (i) divide data into two or more partial data, (ii) insert virtual network access information into each of the divided two or more partial data, and (iii) then transmit the divided two or more partial data to a reception device over two or more networks in a heterogeneous network. When a problem occurrence is identified in a first network of the two or more networks, the transmission device is configured to switch the first network to another second network of the two or more networks to transmit the divided two or more partial data intended to be transmitted over the first network.