The deal also includes a long-term agreement for coal sale from the mine.
Idemitsu spokesman was quoted by Reuters as saying that Chugoku will purchase around 700,000 tons of coal per year for at least five years.
Boggabri Coal Mine is said to host thermal coal with high calorific value, low sulphur and low ash. For the full year 2014, the mine is estimated to produce around 5.4 million tons.
The completion of the transaction is subject to certain conditions, including the receipt of approval from the relevant authorities.
Idemitsu said: "Given demand for coal has been increasing in Asia including Japan where new coal power plants are being constructed, the mine will increase its production, improve quality of the coal by implementation of Coal Preparation Plant and also increase production of Pulverised Coal Injection Coal and Semi Soft Coking Coal from 2015.
"Furthermore we make efforts to operate the mine in a safe and stable manner and contribute to power and energy supply to Japan."
