A honeycomb catalyst body comprising: a modified honeycomb structure that includes a porous partition wall having a number of pores, the partition wall being disposed to form a plurality of cells through the modified honeycomb structure between two end faces (11 a, 11 b); a catalyst that is supported in a given area of the partition wall; and plugging sections that plug one open end of given cells at one end face (111 a) and the other open end of the remaining cells at the other end face; the modified honeycomb structure including: a first area that includes a modified partition wall and includes at least part of one end face (111 a) of the modified honeycomb structure, a number of particles adhering to an inner surface of pores formed in the modified partition wall; and a second area that includes an unmodified partition wall and includes at least part of the other end face of the modified honeycomb structure, the particles not adhering to the unmodified partition wall; the modified partition wall having a porosity lower than that of the unmodified partition wall; an amount of the catalyst supported in the first area per unit volume being smaller than that of the second area; wherein the first area extends from a center to a periphery of the honeycomb catalyst body in a range corresponding to 2/5 to 1/1 of a radius of the honeycomb catalyst body and extends from the one end face (111 a) of the honeycomb catalyst body along a cell extension direction in a range corresponding to 1/10 to 1/2 of a total length of the honeycomb catalyst body. a modified honeycomb structure that includes a porous partition wall having a number of pores, the partition wall being disposed to form a plurality of cells through the modified honeycomb structure between two end faces (11 a, 11 b); a catalyst that is supported in a given area of the partition wall; and plugging sections that plug one open end of given cells at one end face (111 a) and the other open end of the remaining cells at the other end face; the modified honeycomb structure including: a first area that includes a modified partition wall and includes at least part of one end face (111 a) of the modified honeycomb structure, a number of particles adhering to an inner surface of pores formed in the modified partition wall; and a second area that includes an unmodified partition wall and includes at least part of the other end face of the modified honeycomb structure, the particles not adhering to the unmodified partition wall; the modified partition wall having a porosity lower than that of the unmodified partition wall; an amount of the catalyst supported in the first area per unit volume being smaller than that of the second area; wherein the first area extends from a center to a periphery of the honeycomb catalyst body in a range corresponding to 2/5 to 1/1 of a radius of the honeycomb catalyst body and extends from the one end face (111 a) of the honeycomb catalyst body along a cell extension direction in a range corresponding to 1/10 to 1/2 of a total length of the honeycomb catalyst body. a first area that includes a modified partition wall and includes at least part of one end face (111 a) of the modified honeycomb structure, a number of particles adhering to an inner surface of pores formed in the modified partition wall; and a second area that includes an unmodified partition wall and includes at least part of the other end face of the modified honeycomb structure, the particles not adhering to the unmodified partition wall; the modified partition wall having a porosity lower than that of the unmodified partition wall; an amount of the catalyst supported in the first area per unit volume being smaller than that of the second area; wherein the first area extends from a center to a periphery of the honeycomb catalyst body in a range corresponding to 2/5 to 1/1 of a radius of the honeycomb catalyst body and extends from the one end face (111 a) of the honeycomb catalyst body along a cell extension direction in a range corresponding to 1/10 to 1/2 of a total length of the honeycomb catalyst body.