A honeycomb structure body comprising: a plurality of honeycomb segments having porous partition walls with which a plurality of cells extending from one end surface to the other end surface to become through channels of a fluid are formed, and an outer peripheral wall positioned at the outermost periphery and disposed to surround the partition walls, and having plugged portions arranged in one end portion of each of predetermined cells and the other end portion of each of the remaining cells; and joining material layers having a plurality of pores and joining the plurality of honeycomb segments in a state where the honeycomb segments are arranged adjacent to each other so that side surfaces of the honeycomb segments face each other, characterized in that the ratio of the number of pores having a value of 1.2 or less which is obtained by dividing a maximum diameter of each of the pores by a minimum diameter of the each of the pores is 60% or more of the number of all the pores of each of the joining material layers, wherein in the calculation of said ratio the pores are analysed by image processing of an electron micrograph of a cross section of the joining material layer perpendicular to the thickness direction of the layer and the number of all pores and the number of pores having a value of the maximum diameter divided by the minimum diameter of 1.2 or less are counted and wherein in said calculation of said ratio pores having an area smaller than 50 μm 2 are excluded; wherein an average pore diameter of the joining material layer is from 20 to 50 μm, and the joining material layers are formed by firing a joining material composition containing a pore former, wherein the pore former comprises 4 to 6 mass% of the total amount of solid content of the joining material composition, wherein the pore former is a resin balloon. a plurality of honeycomb segments having porous partition walls with which a plurality of cells extending from one end surface to the other end surface to become through channels of a fluid are formed, and an outer peripheral wall positioned at the outermost periphery and disposed to surround the partition walls, and having plugged portions arranged in one end portion of each of predetermined cells and the other end portion of each of the remaining cells; and joining material layers having a plurality of pores and joining the plurality of honeycomb segments in a state where the honeycomb segments are arranged adjacent to each other so that side surfaces of the honeycomb segments face each other, characterized in that the ratio of the number of pores having a value of 1.2 or less which is obtained by dividing a maximum diameter of each of the pores by a minimum diameter of the each of the pores is 60% or more of the number of all the pores of each of the joining material layers, wherein in the calculation of said ratio the pores are analysed by image processing of an electron micrograph of a cross section of the joining material layer perpendicular to the thickness direction of the layer and the number of all pores and the number of pores having a value of the maximum diameter divided by the minimum diameter of 1.2 or less are counted and wherein in said calculation of said ratio pores having an area smaller than 50 μm 2 are excluded; wherein an average pore diameter of the joining material layer is from 20 to 50 μm, and the joining material layers are formed by firing a joining material composition containing a pore former, wherein the pore former comprises 4 to 6 mass% of the total amount of solid content of the joining material composition, wherein the pore former is a resin balloon.