Provided are a data transmission apparatus and method for transmitting data in a Delay-Insensitive (DI) data transmission method supporting a handshake protocol. The data transmission apparatus includes a sender which outputs a binary-valued logic signal based on binary-valued logic, and an encoder which encodes the binary-valued logic signal input through input wires into a multi-valued logic signal based on multi-valued logic and transmits the encoded multi-valued logic signal to a decoder through output wires. Here, the encoder includes a mapping table which stores input variables including the number of input wires and the number of output wires smaller than the number of input wires and the multi-valued logic signal corresponding to the input variables, and encodes the binary-valued logic signal into the multi-valued logic signal with reference to the mapping table.