A pair of adjacent rolled steel sheet piles, each sheet pile having a hat-shape in cross-section and comprising: a first end flange; a second end flange; a first web and a second web to which said first and second end flanges are connected respectively; a central flange to which said first and second webs are connected respectively; a first joint portion formed at an edge of said first end flange; and a second joint portion formed at an edge of said second end flange, wherein a cross-sectional shape of each steel sheet pile is line-symmetric with respect to a central line perpendicular to the central flange at the center thereof except for the joints; each of said first and second joint portions, which are formed by bending inward, including a connecting portion, a bottom portion, and an engaging edge portion, the connecting portion, the bottom portion and the engaging edge portion forming an approximately trapezoidal and tapered-off fitting groove, a protrusion, which prevents the first and second joint portions from rotation, being formed on a fitting groove side of the connecting portion, and wherein the engaging edge portion widening toward an end thereof is for being received into a fitting groove of said adjacent rolled sheet pile to form an interfitted joint, wherein a cross-sectional shape of said first and second joint portions is point-symmetric, and said first and second joint portions are designed so that a center of a point of symmetry of the interfitted joint is located on centerlines of said first and second end flanges, of the first and second steel pile, respectively, in a thickness direction, wherein the fitting grooves of said first and second joint portions of the same sheet pile open in opposite directions, said first and second joint portions are located so that the cross-sections of said first and second joint portions are point-symmetric, said first and second end flanges of said sheet pile are connected to first and second webs, respectively, and the first and second webs are connected to each other via the central flange located therebetween, when said adjacent rolled steel sheet piles are interlocked to form a pair of interfitted or interlocked joints, a central line of a point of symmetry of the pair of interfitted joints is located on centerlines of said first and second end flanges, of respective steel sheet piles, in the thickness direction, and the distance from each part of said first and second joints, where a bending moment/stress is concentrated, to a point of a load vector is minimized, said bending moment being calculated by multiplying a load by the distance from each part of the joint to the point of the load vector. a first end flange; a second end flange; a first web and a second web to which said first and second end flanges are connected respectively; a central flange to which said first and second webs are connected respectively; a first joint portion formed at an edge of said first end flange; and a second joint portion formed at an edge of said second end flange, wherein a cross-sectional shape of each steel sheet pile is line-symmetric with respect to a central line perpendicular to the central flange at the center thereof except for the joints; each of said first and second joint portions, which are formed by bending inward, including a connecting portion, a bottom portion, and an engaging edge portion, the connecting portion, the bottom portion and the engaging edge portion forming an approximately trapezoidal and tapered-off fitting groove, a protrusion, which prevents the first and second joint portions from rotation, being formed on a fitting groove side of the connecting portion, and wherein the engaging edge portion widening toward an end thereof is for being received into a fitting groove of said adjacent rolled sheet pile to form an interfitted joint, wherein a cross-sectional shape of said first and second joint portions is point-symmetric, and said first and second joint portions are designed so that a center of a point of symmetry of the interfitted joint is located on centerlines of said first and second end flanges, of the first and second steel pile, respectively, in a thickness direction, wherein the fitting grooves of said first and second joint portions of the same sheet pile open in opposite directions, said first and second joint portions are located so that the cross-sections of said first and second joint portions are point-symmetric, said first and second end flanges of said sheet pile are connected to first and second webs, respectively, and the first and second webs are connected to each other via the central flange located therebetween, when said adjacent rolled steel sheet piles are interlocked to form a pair of interfitted or interlocked joints, a central line of a point of symmetry of the pair of interfitted joints is located on centerlines of said first and second end flanges, of respective steel sheet piles, in the thickness direction, and the distance from each part of said first and second joints, where a bending moment/stress is concentrated, to a point of a load vector is minimized, said bending moment being calculated by multiplying a load by the distance from each part of the joint to the point of the load vector.