Provided is a novel catalyst structure capable of maintaining gas diffusivity to a deep part of a catalyst layer even under condition of a high gas flow rate. Proposed is a catalyst structure, which has a porous apatite catalyst layer containing an oxide (hereinafter referred to as “apatite”) whose crystalline structure belongs to an apatite type, and in which, in logarithmic differentiation void volume distribution measured by a mercury intrusion porosimeter, a peak top is present within a void volume diameter range of 100 nm to 1000 nm.