The invention relates to the cocurrent gasification of coal and to a gas generator. The gas generator (11) comprises a vertical sealed vessel, the lower third of which is divided into several identical vertical compartments (12). Coal is loaded at the top (17). The major part of the hot reactive gas under pressure is introduced at the top (18), and the remaining part at lower levels (21, 22). Gas evacuation (24) is stopped from one compartment (12) in turn, gas produced is blown in order to unclog the filters (25, 26) and to loosen the ash, the ash is extracted at the bottom (23) and cold reactive gas is blown countercurrently in order to complete the combustion and to cool the ash. This gas generator enables coal from any source to be used and does not require purification downstream.