To improve strength, rigidity, water-sealing properties or the like by a simple constitution by ensuring the joint-fitting interrupting slit section of a succeeding steel sheet pile in the flange section of a steel sheet pile configuring a mortar-fitting joint and organizing a pocket for filling mortar by joining and extending wing pieces so as to surround the joint.

In the U-shaped steel sheet pipe 7 having joints 2 at the front ends of flanges 6 on both sides of webs 5, one end 10 of L-steel (an angle wing piece) is fixed onto one flange 6 by welding 11 so as to surround the joint 2, and a pocket 12 for filling mortar is constituted between the flange 6 and the angle wing piece 8. One end section 10 of the angle wing piece 8 is fastened onto the flange 6 of the U-shaped steel sheet pile 7 by welding 11, but a front end section 13 is positioned at the outer edge of the joint 2 adjacently or in a contacting degree so as not to prevent interruption to the pocket 13 for filling mortar in case of the fitting of the joint 2 of a succeeding steel sheet pile 7, and the joint-fitting interruption slit of the succeeding steel sheet pile 7 is ensured.