To prevent scouring of a trail up a mountain by a flowing-down water current.

A footstep is formed with a concrete block in a nearly reverse U-shape. The concrete block consists of a rectangular shaped horizontal top board part 1, and a sidewall part 3 and a sidewall part 2 hung down from both opposed sides of the top board. The sidewall part 3 is located to a mountainside of a trail up a mountain. The sidewall part 2 is located to a valley side of the trail up the mountain, and is higher than the sidewall of the mountainside. Furthermore, openings 4 are formed on the top board, and openings 5 are formed on the sidewall part of the mountainside.