A flange structure for connecting together two members each having a flow path with different angles which can control an increase in flow resistance and can realize easy and stable manufacture can include a first member and a second member connected to each other through a flange. A central axis of a flow path of the second member can be slanted at a first angle with respect to a central axis of a flow path of the first member. The flow path of the first member and the flow path of the second member are allowed to communicate with each other by an in-flange flow path formed in the flange, and a second angle constituted of an acute angle between a central axis of the in-flange flow path and the central axis of the flow path of the first member is smaller than the first angle.