To provide a movable guard rail system which detects contact or proximity between a movable guard rail and a side wall in a highly reliable mode by using metal detecting sensors and metal members even if an ambient temperature is largely changed.

The movable guard rail system is composed of: the movable guard rail 40 arranged on a road having the side wall 22, having a turning shaft that is almost perpendicular to the road, at a rear edge thereof, and having a front edge 43 that is brought into contact with or close to the side wall when turned toward the side wall; recesses 47, 48 arranged at the front edge 43 of the movable guard rail 40, and each having a tapered shape that is formed so as to be larger in a cross sectional area on an entrance side than on a back side; the metal detecting sensors 17, 18 arranged in the recesses 47, 48, respectively; and the metal members 15, 16 arranged on the side wall 22, and having tapered shapes corresponding to the tapered shapes of the recesses 47, 48, respectively. Herein the metal members 15, 16 are mounted on the side wall 22 in a displaceable manner.