Provided is a novel catalyst structure which can sustain gas diffusivity into a deep part of a catalyst layer even under conditions with a high gas flow rate. Proposed is a catalyst structure provided with a porous apatite catalyst layer, said porous apatite catalyst layer comprising an oxide that has an apatite type crystalline structure (hereinafter referred to as "apatite"), characterized in that, in the logarithmic differentiation void volume distribution measured with a mercury intrusion porosimeter, a peak top is present within a void volume size range of 100-1000 nm.