PURPOSE: To improve the safety by relaxing an impact force during collision and sufficiently absorbing collision energy.

CONSTITUTION: Bead 31 being a recessed part to induce initial buckling are respectively formed on the tip part sides of the upper frames 20 and 21 of a car body of a strength member on which a squeeze load is exerted and buckle heads 32, 33, and 34 serving as a plurality of partition walls are arranged at a portion ranging from the bead 31 to the rear end part sides of the upper frames 20 and 21. A distance S between the bead 31 and the buckle heads 32 and distances between the adjoining buckle heads 32, 33, and 34 are set to a value lower than a value two times as large as a buckle pitch P inherent to the upper plates 20 and 21.