A lower limb protecting air bag includes: a main body inflation part; an end side inflation part; a bending part configured to bend the end side inflation part to project backward from the main body inflation part in inflation completion; and a connecting element configured to connect together the end side inflation part and the main body inflation part so that the bent state of the end side inflation part in inflation completion is maintained, wherein: the main body inflation part and the end side inflation part are configured to inflate substantially in a plate shape to separate a front side wall disposed on the back side and a back side wall disposed on the front side when the air bag is developed flat; and the bending part includes a seam part formed by superimposing and connecting together the front side wall and the back side wall.