A fuel cell system comprising: a casing having a suction port through which air is introduced from outside into an internal space thereof; a fuel cell accommodated within the casing and configured to generate electric power through an electrochemical reaction between a fuel gas and an oxidizing gas; an air supply unit of a diaphragm type disposed within the casing and configured to take in the air introduced through the suction port and supply the air to the fuel cell; a heating unit disposed within the casing and configured to heat the air in a space from the suction port to the air supply unit; a separating plate for separating the internal space of the casing into an upper space and a lower space, the separating plate having a communication port via which the upper space and the lower space are communicated with each other; a fuel gas generating device for generating a fuel gas supplied to the fuel cell, using a raw material and water; and a water circuit including a condensed water recovery passage for recovering condensed water from at least one of an off-gas from an anode of the fuel cell, an off-gas from a cathode of the fuel cell, and an off-gas from the fuel gas generating device; and a water tank disposed in the upper space to store the condensed water; wherein the fuel cell, the fuel gas generating device, and the air supply unit are disposed within the upper space, and the air supply unit is communicated with the lower space via the communication port; wherein the lower space forms an air introduction space through which the air introduced from the suction port flows to the communication port, wherein the heating unit is disposed in the air introduction space; and wherein the separating plate has a penetrating section via which the upper space and the air introduction space are communicated with each other to supply the air within the air introduction space which is heated by the heating unit, to at least a portion of the water circuit positioned in the upper space. a casing having a suction port through which air is introduced from outside into an internal space thereof; a fuel cell accommodated within the casing and configured to generate electric power through an electrochemical reaction between a fuel gas and an oxidizing gas; an air supply unit of a diaphragm type disposed within the casing and configured to take in the air introduced through the suction port and supply the air to the fuel cell; a heating unit disposed within the casing and configured to heat the air in a space from the suction port to the air supply unit; a separating plate for separating the internal space of the casing into an upper space and a lower space, the separating plate having a communication port via which the upper space and the lower space are communicated with each other; a fuel gas generating device for generating a fuel gas supplied to the fuel cell, using a raw material and water; and a water circuit including a condensed water recovery passage for recovering condensed water from at least one of an off-gas from an anode of the fuel cell, an off-gas from a cathode of the fuel cell, and an off-gas from the fuel gas generating device; and a water tank disposed in the upper space to store the condensed water; wherein the fuel cell, the fuel gas generating device, and the air supply unit are disposed within the upper space, and the air supply unit is communicated with the lower space via the communication port; wherein the lower space forms an air introduction space through which the air introduced from the suction port flows to the communication port, wherein the heating unit is disposed in the air introduction space; and wherein the separating plate has a penetrating section via which the upper space and the air introduction space are communicated with each other to supply the air within the air introduction space which is heated by the heating unit, to at least a portion of the water circuit positioned in the upper space.