A honeycomb structural body comprising: a pillar-shaped ceramic block made of porous ceramic which includes a number of through holes that are placed in parallel with one another in the length direction with a wall portion interposed therebetween; and a sealing material provided on an outer peripheral portion of said pillar-shaped ceramic block, each of said honeycomb structural body and said pillar-shaped ceramic block having irregularities formed on an outer peripheral face thereof, wherein: when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said honeycomb structural body, a center-of-gravity thereof is defined as c1, a distance between a minimum concentric circumscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D1, a distance between a maximum concentric inscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D2, and (D1 - D2) is defined as M1, the following inequality is satisfied: 0.3 mm ≤ M1; and when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said ceramic block, a center-of-gravity thereof is defined as c2, a distance between a minimum concentric circumscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D3, a distance between a maximum concentric inscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D4, and (D3 - D4) is defined as M2, the following inequality is satisfied: 0.5 mm ≤ M2 ≤ 7.0 mm. a pillar-shaped ceramic block made of porous ceramic which includes a number of through holes that are placed in parallel with one another in the length direction with a wall portion interposed therebetween; and a sealing material provided on an outer peripheral portion of said pillar-shaped ceramic block, each of said honeycomb structural body and said pillar-shaped ceramic block having irregularities formed on an outer peripheral face thereof, wherein: when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said honeycomb structural body, a center-of-gravity thereof is defined as c1, a distance between a minimum concentric circumscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D1, a distance between a maximum concentric inscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D2, and (D1 - D2) is defined as M1, the following inequality is satisfied: 0.3 mm ≤ M1; and when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said ceramic block, a center-of-gravity thereof is defined as c2, a distance between a minimum concentric circumscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D3, a distance between a maximum concentric inscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D4, and (D3 - D4) is defined as M2, the following inequality is satisfied: 0.5 mm ≤ M2 ≤ 7.0 mm. when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said honeycomb structural body, a center-of-gravity thereof is defined as c1, a distance between a minimum concentric circumscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D1, a distance between a maximum concentric inscribed curve, having c1 as the center-of-gravity, of said least square curve and the center-of-gravity c1 is defined as D2, and (D1 - D2) is defined as M1, the following inequality is satisfied: 0.3 mm ≤ M1; and when a least square curve is determined by a least square method on the basis of points constituting the contour of a cross-section perpendicular to the length direction of said ceramic block, a center-of-gravity thereof is defined as c2, a distance between a minimum concentric circumscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D3, a distance between a maximum concentric inscribed curve, having c2 as the center-of-gravity, of said least square curve and the center-of-gravity c2 is defined as D4, and (D3 - D4) is defined as M2, the following inequality is satisfied: 0.5 mm ≤ M2 ≤ 7.0 mm.