Accompanying gradual increase of consuming coal as inexpensive energy, a great deal of coal which has tendency to generate methane-gas spontaneously by oxidizing heat is transported overseas by many bulk carriers. The problem of methane-gas generation originating from coal self-heating is induced greatly the concern in the coal transportation as bulk cargo for the reason that the accidents of gas explosion is apprehensive to occur. Consequently, it needs to take counter-measures to cope with preventing from accumulating surplus explosive gas beyond the lower limit of explosive concentration in void spaces of cargo holds. For this purpose, the hold ventilation is a way of controlling the gas concentration to take account into the fact that quantity of oxidizing heat of fine coal depends upon its temperature and surrounding oxygen concentration which could be expressed by the Arrheniuse's formula. The generated methane-gas by oxidizing heat of stored coal and the variation of gas concentration in cargo hold with ventilation are clarified in the present study. Firstly, the measurement of generating quantity of methane-gas based on coal temperature is carried out experimentally using the gas-tight steel box in the electric furnace. Secondly, the variation of temperature and gas concentration in a cargo hold are simulated numerically for the coals having combined properties of thermal and gas characteristic, by using the thermal conductivity equation and the gas diffusion equations with the selfgenerating source. By the results of simulation, the gas accumulation in a cargo hold must depend upon the properties of coal in regard to methane-gas generation and it may be difficult to control the gas concentration within the safety range only by hold ventilation in a case of carrying the coal with high gas generation.