The present invention aims to provide a method of regenerating foundry sand whereby the carbon component adhering to the surface of spent foundry sand and similar substances is combusted efficiently, allowing the foundry sand to be regenerated at low cost. In the present invention, in order to achieve this aim the spent foundry sand with the carbon component adhering to it is placed in a combustion furnace which is connected on one side to a pressure-reducing pump and is open on the other, the pressure-reducing pump is operated to draw air from within the foundry sand and introduce air into it, and the accretion is ignited upwind of the current of air which is being introduced, allowing combustion of the accretion to proceed successively on the downwind side. Foundry sand can thus be recycled at very low cost, simply and reliably because it is allowed to self-combust continuously without any heating or agitation from elsewhere, and because the resin is combusted entirely.