A honeycomb structure defect inspection device for a plugged honeycomb structure comprising a cell structure portion constituted of partition walls (13,13a,13b,13c) disposed to form a plurality of cells (12, 12a, 12b, 12c, 12d) extending through the structure in an axial direction and an outer peripheral wall disposed along the outer periphery of the cell structure portion, the honeycomb structure defect inspection device comprising: a defect detection means for introducing a detection medium into cells (12, 12a, 12b, 12c, 12d) from one end face of the plugged honeycomb structure in the axial direction, while applying a pressure to the detection medium to detect defects of the partition walls constituting the cells (12, 12a, 12b, 12c, 12d), and detecting the detection medium passed through the cells (12, 12a, 12b, 12c, 12d) and discharged from the other end face of the structure to identify the cell (12, 12a, 12b, 12c, 12d) constituted of the partition wall having the defect from the dynamic state of the detection medium discharged from the cells in the other end face of the plugged honeycomb structure; wherein the detection medium comprises particles contained in a gas, and the detection of the dynamic state of the detection medium comprises judgment of luminance found by measuring the intensity of light scattered by the particles, characterized by an outer peripheral wall covering means for covering 35% or more of the outer peripheral wall so as to maintain the pressure which causes the detection medium in the cells (12, 12a, 12b, 12c, 12d) to flow toward the other end face while suppressing the leakage of the pressure from the outer peripheral wall and so as to sufficiently keep the discharge of the detection medium from the cells (12, 12a, 12b, 12c, 12d) constituted of the partition walls which do not have any defect in the vicinity of the outer peripheral wall in the other end face. a defect detection means for introducing a detection medium into cells (12, 12a, 12b, 12c, 12d) from one end face of the plugged honeycomb structure in the axial direction, while applying a pressure to the detection medium to detect defects of the partition walls constituting the cells (12, 12a, 12b, 12c, 12d), and detecting the detection medium passed through the cells (12, 12a, 12b, 12c, 12d) and discharged from the other end face of the structure to identify the cell (12, 12a, 12b, 12c, 12d) constituted of the partition wall having the defect from the dynamic state of the detection medium discharged from the cells in the other end face of the plugged honeycomb structure; wherein the detection medium comprises particles contained in a gas, and the detection of the dynamic state of the detection medium comprises judgment of luminance found by measuring the intensity of light scattered by the particles, characterized by an outer peripheral wall covering means for covering 35% or more of the outer peripheral wall so as to maintain the pressure which causes the detection medium in the cells (12, 12a, 12b, 12c, 12d) to flow toward the other end face while suppressing the leakage of the pressure from the outer peripheral wall and so as to sufficiently keep the discharge of the detection medium from the cells (12, 12a, 12b, 12c, 12d) constituted of the partition walls which do not have any defect in the vicinity of the outer peripheral wall in the other end face.