A solid-oxide fuel cell system comprising: a fuel cell unit (12, 112) including a solid-oxide fuel cell (10, 110) including an anode gas channel (16, 116) and a cathode gas channel (20, 120), and a mixer (24, 124) configured to mix an anode off gas discharged from the anode gas channel (16, 116) and a cathode off gas discharged from the cathode gas channel (20, 120); an electric power generation raw material supplier (14, 114) configured to supply an electric power generation raw material to the fuel cell unit (12, 112); a combustible gas channel (18, 118) extending from the electric power generation raw material supplier (14, 114) to a downstream end of the anode gas channel (16, 116); an oxidizing gas supplier (22, 122) configured to supply an oxidizing gas to the cathode gas channel (20, 120); and a controller (50, 150), wherein, after electric power generation of the fuel cell unit (12, 112) is stopped, the controller (50, 150) is configured to control the electric power generation raw material supplier (14, 114) to supply to the combustible gas channel (18, 118) such that a volume of the electric power generation raw material supplied to the combustible gas channel (18, 118) becomes less than a volume of the combustible gas channel (18, 118), and the amount of the electric power generation raw material supplied compensates for contraction of a gas in the combustible gas channel (18, 118) due to temperature decrease of the fuel cell unit (12, 112) and also control the oxidizing gas supplier (22, 122) to supply the oxidizing gas to the cathode gas channel (20, 120) in accordance with the supply of the electric power generation raw material, the electric power generation raw material is a substance containing an organic compound whose constituent elements are at least carbon and hydrogen, and a period in which the supply of the electric power generation raw material is executed and a period in which the supply of the oxidizing gas is executed at least partially overlap each other. a fuel cell unit (12, 112) including a solid-oxide fuel cell (10, 110) including an anode gas channel (16, 116) and a cathode gas channel (20, 120), and a mixer (24, 124) configured to mix an anode off gas discharged from the anode gas channel (16, 116) and a cathode off gas discharged from the cathode gas channel (20, 120); an electric power generation raw material supplier (14, 114) configured to supply an electric power generation raw material to the fuel cell unit (12, 112); a combustible gas channel (18, 118) extending from the electric power generation raw material supplier (14, 114) to a downstream end of the anode gas channel (16, 116); an oxidizing gas supplier (22, 122) configured to supply an oxidizing gas to the cathode gas channel (20, 120); and a controller (50, 150), wherein, after electric power generation of the fuel cell unit (12, 112) is stopped, the controller (50, 150) is configured to control the electric power generation raw material supplier (14, 114) to supply to the combustible gas channel (18, 118) such that a volume of the electric power generation raw material supplied to the combustible gas channel (18, 118) becomes less than a volume of the combustible gas channel (18, 118), and the amount of the electric power generation raw material supplied compensates for contraction of a gas in the combustible gas channel (18, 118) due to temperature decrease of the fuel cell unit (12, 112) and also control the oxidizing gas supplier (22, 122) to supply the oxidizing gas to the cathode gas channel (20, 120) in accordance with the supply of the electric power generation raw material, the electric power generation raw material is a substance containing an organic compound whose constituent elements are at least carbon and hydrogen, and a period in which the supply of the electric power generation raw material is executed and a period in which the supply of the oxidizing gas is executed at least partially overlap each other.