To provide a gas supply system for avoiding the event that a safety valve is operated with the rise of inner pressure of a bulk storage tank storing liquefied gas in a summer season.

Medium in a heat exchanger 35 is heat-exchanged and heated with the combustion heat of a combustion part 34 and circulated and supplied to a coil tube 41 via a circuit 42 to heat the liquefied gas Q in the bulk storage tank 2. Vaporized gas by the heat is supplied with the gas supply system 5. When the inner pressure of the bulk storage tank rises with the temperature rise of the liquefied gas following the temperature rise of outside air to reach a set pressure, cooling operation is performed until it gets down to a preset pressure. In the cooling operation, a pump 43 and a blowing fan 33 are operated in the non-combustible condition of the combustion part to forcibly radiate the heat of the medium being circulated in the circuit to be cooled through the heat exchanger 35. While the cooled medium passes through the coil tube, it is heat-exchanged with the liquefied gas to be cooled.