A honeycomb structure includes a central area and a reinforced outer peripheral area. A reference boundary cell with an inner wall orthogonal to an imaginary straight line, adjacent to the honeycomb center, and thinner than an outer wall adjacent to the honeycomb periphery has a reference wall different in wall thickness from the other three cell walls among the remaining four cell walls excluding the inner wall and the outer wall. The honeycomb structure includes a reference Y-shaped unit having the reference wall, the outer wall, and a cell wall. The honeycomb structure includes a plurality of Y-shaped units extending in the same directions as the reference Y-shaped unit. For every Y-shaped unit in the central area and the reinforced outer peripheral area of the honeycomb structure, the cell walls of each Y-shaped unit has an equal wall thickness.