An inside air control system, comprising: a gas supply device; and a gas mixture generator that generates a gas mixture having a higher nitrogen concentration and a lower oxygen concentration than air sucked through a filter unit of the gas supply device, wherein gas generated by the gas mixture generator is supplied to a target space using the air pump, the gas supply device comprising: a gas passage that supplies air to a target space; a filter unit provided at an inlet of the gas passage; and an air pump provided in the middle of the gas passage, characterized in that the filter unit comprises: a filter box; and an air filter housed in the filter box, wherein the air filter is arranged to be spaced apart from wall surfaces of the filter box, an air intake port is formed in an air intake surface, which is one of surfaces of the filter box, and a space which is present between the air intake surface provided with the air intake port and an air inflow surface of the air filter corresponding to the air intake surface is a primary space through which the air flows into the air filter, and a plurality of spaces, each of which is present between one of surfaces of the air filter other than the air inflow surface and an associated one of the wall surfaces of the filter box, are secondary spaces into each of which the air flows out from the air filter. a gas supply device; and a gas mixture generator that generates a gas mixture having a higher nitrogen concentration and a lower oxygen concentration than air sucked through a filter unit of the gas supply device, wherein gas generated by the gas mixture generator is supplied to a target space using the air pump, the gas supply device comprising: a gas passage that supplies air to a target space; a filter unit provided at an inlet of the gas passage; and an air pump provided in the middle of the gas passage, characterized in that the filter unit comprises: a filter box; and an air filter housed in the filter box, wherein the air filter is arranged to be spaced apart from wall surfaces of the filter box, an air intake port is formed in an air intake surface, which is one of surfaces of the filter box, and a space which is present between the air intake surface provided with the air intake port and an air inflow surface of the air filter corresponding to the air intake surface is a primary space through which the air flows into the air filter, and a plurality of spaces, each of which is present between one of surfaces of the air filter other than the air inflow surface and an associated one of the wall surfaces of the filter box, are secondary spaces into each of which the air flows out from the air filter. a gas passage that supplies air to a target space; a filter unit provided at an inlet of the gas passage; and an air pump provided in the middle of the gas passage, a filter box; and an air filter housed in the filter box, wherein the air filter is arranged to be spaced apart from wall surfaces of the filter box, an air intake port is formed in an air intake surface, which is one of surfaces of the filter box, and a space which is present between the air intake surface provided with the air intake port and an air inflow surface of the air filter corresponding to the air intake surface is a primary space through which the air flows into the air filter, and a plurality of spaces, each of which is present between one of surfaces of the air filter other than the air inflow surface and an associated one of the wall surfaces of the filter box, are secondary spaces into each of which the air flows out from the air filter.