A fuel cell apparatus, comprising: a housing including a power generation chamber and a closing member (201, 202) closing an upper portion of the power generation chamber; a stack provided in the power generation chamber and supplied with an anode gas and a cathode gas to generate electric power; a cathode gas flow passage provided at the housing and allowing the cathode gas to be supplied to the stack; an exhaust gas flow passage provided at the housing and allowing an exhaust gas generated at the power generation chamber to be exhausted to an outside of the power generation chamber; the housing including a first U-shaped plate member which is formed in a U-shape and includes a first upper surface opening portion opening upwardly in a height direction of the housing, two first side walls facing each other, a first bottom wall connecting a lower portion of each of the two first side walls to each other; the housing including a second U-shaped plate member which is formed in a U-shape and includes a second upper surface opening portion opening upwardly in the height direction, two second side walls facing each other, a second bottom wall connecting a lower portion of each of the two second side walls to each other; the housing being formed by layering the first U-shaped plate member and the second U-shaped plate member with each other while a clearance being provided between the first U-shaped plate member and the second U-shaped plate member in a thickness direction thereof in a manner that the first upper surface opening portion and the second upper surface opening portion are positioned at an upper side in the height direction; and at least part of at least one of the cathode gas flow passage and the exhaust gas flow passage including a side clearance flow passage (510, 610) formed by one of the two first side walls and one of the two second side walls which faces the one of the two first side walls in a thickness direction thereof, and a bottom clearance flow passage (520, 620) formed by the first bottom wall and the second bottom wall which face each other, the bottom clearance flow passage (520, 620) being in fluid communication with the side clearance flow passage (510, 610), characterized in that each of the first side walls and the second side walls is provided with a ribbed-and-raised portion (212r, 222r) including a recess (212s, 222s), the ribbed-and-raised portion (212r, 222r) including the recess (212s, 222s) being formed to be extended continuously in a lengthwise direction of the first U-shaped plate member and the second U-shaped plate member. a housing including a power generation chamber and a closing member (201, 202) closing an upper portion of the power generation chamber; a stack provided in the power generation chamber and supplied with an anode gas and a cathode gas to generate electric power; a cathode gas flow passage provided at the housing and allowing the cathode gas to be supplied to the stack; an exhaust gas flow passage provided at the housing and allowing an exhaust gas generated at the power generation chamber to be exhausted to an outside of the power generation chamber; the housing including a first U-shaped plate member which is formed in a U-shape and includes a first upper surface opening portion opening upwardly in a height direction of the housing, two first side walls facing each other, a first bottom wall connecting a lower portion of each of the two first side walls to each other; the housing including a second U-shaped plate member which is formed in a U-shape and includes a second upper surface opening portion opening upwardly in the height direction, two second side walls facing each other, a second bottom wall connecting a lower portion of each of the two second side walls to each other; the housing being formed by layering the first U-shaped plate member and the second U-shaped plate member with each other while a clearance being provided between the first U-shaped plate member and the second U-shaped plate member in a thickness direction thereof in a manner that the first upper surface opening portion and the second upper surface opening portion are positioned at an upper side in the height direction; and at least part of at least one of the cathode gas flow passage and the exhaust gas flow passage including a side clearance flow passage (510, 610) formed by one of the two first side walls and one of the two second side walls which faces the one of the two first side walls in a thickness direction thereof, and a bottom clearance flow passage (520, 620) formed by the first bottom wall and the second bottom wall which face each other, the bottom clearance flow passage (520, 620) being in fluid communication with the side clearance flow passage (510, 610),