To efficiently collect methane gas by transferring heat energy without heat loss from the sea or land to a bed reserving methane hydrate and heating methane hydrate.

An underground reserve hydrocarbon gas resource collection system comprises a laser oscillator installed on a floating marine structure or the ground, an optical fiber 1 passed through a tube 2 to lead a laser beam output from the laser oscillator to a bed B reserving methane hydrate, and means for supplying fluid (water, seawater, gas) to the bed B via a clearance between the tube 2 and the optical fiber 1. The laser beam heats the bed B reserving methane hydrate to crush rock, crack methane hydrate and separate methane gas, whereupon the methane gas and crushed rock are collected along with water or seawater.