A catalytic reactor comprising: a reaction-side flow channel in which a reaction fluid is configured to flow, extending in an extending direction defining a flow direction of the reaction fluid; a first structured catalyst and a second structured catalyst located in the reaction-side flow channel and arranged in the extending direction of the reaction-side flow channel; wherein the first structured catalyst includes a first inclined surface in at least part of a surface of the first structured catalyst facing the second structured catalyst, the second structured catalyst includes a second inclined surface facing the first inclined surface, in at least part of a surface of the second structured catalyst facing the first structured catalyst, and the first inclined surface and the second inclined surface are inclined in the same direction with respect to an arrangement direction of the first structured catalyst and the second structured catalyst, characterized in that the first structured catalyst and the second structured catalyst are tilted in the same direction with respect to the arrangement direction in a state where at least part of the first inclined surface and at least part of the second inclined surface are in contact with each other, part of the first structured catalyst on a first inclined surface side is pushed up in a height direction orthogonal to the extending direction and tilted with respect to the extending direction by the at least part of the second inclined surface which presses the at least part of the first inclined surface, so that the first structured catalyst is brought into contact with an inner surface of the reaction-side flow channel so as to close a clearance (g) between the inner surface of the reaction-side flow channel and the first structured catalyst, and the clearance (g) is a difference between a height of the reaction-side flow channel and a height of the first structured catalyst not tilted in the reaction-side flow channel. a reaction-side flow channel in which a reaction fluid is configured to flow, extending in an extending direction defining a flow direction of the reaction fluid; a first structured catalyst and a second structured catalyst located in the reaction-side flow channel and arranged in the extending direction of the reaction-side flow channel; wherein the first structured catalyst includes a first inclined surface in at least part of a surface of the first structured catalyst facing the second structured catalyst, the second structured catalyst includes a second inclined surface facing the first inclined surface, in at least part of a surface of the second structured catalyst facing the first structured catalyst, and the first inclined surface and the second inclined surface are inclined in the same direction with respect to an arrangement direction of the first structured catalyst and the second structured catalyst, characterized in that the first structured catalyst and the second structured catalyst are tilted in the same direction with respect to the arrangement direction in a state where at least part of the first inclined surface and at least part of the second inclined surface are in contact with each other, part of the first structured catalyst on a first inclined surface side is pushed up in a height direction orthogonal to the extending direction and tilted with respect to the extending direction by the at least part of the second inclined surface which presses the at least part of the first inclined surface, so that the first structured catalyst is brought into contact with an inner surface of the reaction-side flow channel so as to close a clearance (g) between the inner surface of the reaction-side flow channel and the first structured catalyst, and the clearance (g) is a difference between a height of the reaction-side flow channel and a height of the first structured catalyst not tilted in the reaction-side flow channel.