The boiler using a liquid metal as a working medium according to the present invention is comprises: a combustion furnace, in which the working medium is supplied and heated; a heat exchange part, which is connected to the combustion furnace and to which the working medium heated in the combustion furnace is supplied; a heat medium injection part, which is positioned in the heat exchange part; and a supply part, which is connected to the heat exchange part and supplies the heat medium to the heat medium injection part. In the heat exchange part, the heat exchange between the heat medium supplied to the heat medium injection part and the heated working medium is performed. The heat medium reaches high temperature and high pressure states at a threshold point or higher by means of the heat exchange. In addition, the working medium is a liquid metal.