The Japanese utility has paid between 10 billion and 20 billion yen to Japanese trading house Mitsubishi Corp to buy the stake, a company spokesperson said.
"We understand there are various opinions about the project, but we have decided to join it as the 1.2 gigawatts (GW) project is expected to contribute to the stable supply of electricity and economic development in Vietnam," the Shikoku Electric spokesperson said.
The move is part of Shikoku Electric's efforts to expand overseas operations to boost growth. It aims to support the operation of the plant with the know-how derived from its domestic power business, the company said.
After the deal, Mitsubishi holds a 25 percent stake in the project while another Japanese utility, Chugoku Electric Power Co Inc, owns a 20 percent stake.