Abstract: A catalyst supporting body has a porous honeycomb base body having a porosity within a range of 40 to 60 vol. %. The body has a plurality of cells partitioned by cell walls arranged in a lattice-like shape. A coated catalyst layer made of a porous body having a void fraction of void spaces within a range of 53 to 63 vol. % is particularly supported on surfaces of the cell walls and in pores formed in the cell walls by a filling rate of not less than 40 vol. %. In an immersing step of a manufacturing method, a combination of a kind of catalyst slurry and the porous honeycomb base body is selected so that a cumulative-frequency at an intersection point between a pore distribution map and a particle size distribution map becomes not less than 80%. The pore distribution map indicates a relationship between pore sizes of pores in the porous honeycomb base body and a cumulative-frequency of the pores.