An encoding apparatus that converts input digital data and an input clock into three-bit six-state transition encode outputs and outputs them is disclosed. The encoding apparatus has a first state transition control section, second state transition control section, and an output selection section. The first state transition control section changes a state of first data at a positive edge of the input clock. The second state transition control section changes a state of second data at a negative edge of the input clock. The output selection section alternately selects the state of the first state transition control section and the second state transition control section.