To provide a new method of operating a heavy oil tank after coal single firing in a coal-fired power plant.

In the coal-fired power plant including a heavy oil tank No. 1 (1A) and a heavy oil tank No. 2(1B), heavy oil is not stored in the heavy oil tank No. 2(1B), and stored only in the heavy oil tank No. 1 (1A). Heavy oil is supplied from only the heavy oil tank No. 1 (1A) to a power generation boiler after coal single firing, and the empty operation of the heavy oil tank No. 2 (1B) with no heavy oil stored is performed.