To enable unused heavy oil such as oil sand to be inexpensively drilled by using as small investment resources as possible.

A medium lead-in pipe 1 and an oil-well pipe 2 are arranged in a heavy oil stratum A. A high-temperature exhaust gas 5 generated by burning fuel 4 by a combustion device 6 is supplied into the medium lead-in pipe 1, and blown into the heavy oil stratum A, so that the heavy oil stratum A can be heated for the fluidization of the heavy oil. The fluidized heavy oil 8 is pumped up by means of the oil-well pipe 2.