An air supply system, comprising: a non-return valve that allows air to flow from an upstream side to a downstream side, the air having been supplied from a compressor, and moisture and oil contained in the air having been removed from the air by a removal device; a discharge device that opens a section between the compressor and the removal device to an atmosphere when an air pressure downstream of the non-return valve is higher than a predetermined pressure; a regenerative device that supplies the air downstream of the non-return valve in a direction of the discharge device from the non-return valve to the removal device by opening a detour passage arranged in parallel with the non-return valve based on supply of electricity; a switching circuit that receives a value of the air pressure downstream of the non-return valve and supplies electricity to the regenerative device to operate the regenerative device when the value of the air pressure is in a predetermined range; and a pneumatic sensor that outputs voltage corresponding to the air pressure detected on the downstream side of the non-return valve, wherein the switching circuit receives the voltage output by the pneumatic sensor as the value of the air pressure downstream of the non-return valve and supplies electricity to the regenerative device to operate the regenerative device when the received voltage is a predetermined voltage, characterized in that a power line (E63A) that branches from a power line for the pneumatic sensor is connected to the regenerative device, and the switching circuit supplies electricity to the regenerative device by completing the branched power line (E63A). a non-return valve that allows air to flow from an upstream side to a downstream side, the air having been supplied from a compressor, and moisture and oil contained in the air having been removed from the air by a removal device; a discharge device that opens a section between the compressor and the removal device to an atmosphere when an air pressure downstream of the non-return valve is higher than a predetermined pressure; a regenerative device that supplies the air downstream of the non-return valve in a direction of the discharge device from the non-return valve to the removal device by opening a detour passage arranged in parallel with the non-return valve based on supply of electricity; a switching circuit that receives a value of the air pressure downstream of the non-return valve and supplies electricity to the regenerative device to operate the regenerative device when the value of the air pressure is in a predetermined range; and a pneumatic sensor that outputs voltage corresponding to the air pressure detected on the downstream side of the non-return valve, wherein the switching circuit receives the voltage output by the pneumatic sensor as the value of the air pressure downstream of the non-return valve and supplies electricity to the regenerative device to operate the regenerative device when the received voltage is a predetermined voltage, characterized in that a power line (E63A) that branches from a power line for the pneumatic sensor is connected to the regenerative device, and the switching circuit supplies electricity to the regenerative device by completing the branched power line (E63A).