A friction coefficient measurement apparatus for measuring friction between a road surface friction measuring rubber attached strip and a road surface, the measurement apparatus comprising: a road surface friction measuring rubber attached strip being a strip to which a road surface friction measuring rubber is attached; an attaching bolt which attaches the road surface friction measuring rubber attached strip to a portion of the friction coefficient measurement apparatus; an anti-loosening spring washer for anti-loosening the attaching bolt and the bolt head of the attaching bolt; and an attaching bolt insertion opening formed in the road surface friction measuring rubber attached strip; characterised in that: the attaching bolt insertion opening has a shape formed by overlapping circles of different diameter sizes, a diameter of a large-diameter circular part is set larger than a diameter of a bolt head of the attaching bolt and a diameter of a small-diameter circular part is set smaller than the diameter of the bolt head of the attaching bolt and larger than a diameter of a bolt shaft; and a rubber attached strip fall prevention washer is interposed between the attaching bolt anti-loosening spring washer and the bolt head of the attaching bolt, the rubber attached strip fall prevention washer is formed into an annular shape, a notch is formed therein and a plurality of projections which project outward in a radius direction are formed thereon, an opening size of said notch is set smaller than an outer diameter of the shaft of the attaching bolt and a maximum distance between leading ends of the projections is set larger than the diameter of the large-diameter circular part in the attaching bolt insertion opening formed in the road surface friction measuring rubber attached strip, and the notch in the rubber attached strip fall prevention washer can be manually forced open by elastic deformation to allow the bolt shaft of the attaching bolt to be inserted into the forced-open notch, after which the size of the opening of the notch will return to a state where it is smaller than the diameter size of the bolt shaft. a road surface friction measuring rubber attached strip being a strip to which a road surface friction measuring rubber is attached; an attaching bolt which attaches the road surface friction measuring rubber attached strip to a portion of the friction coefficient measurement apparatus; an anti-loosening spring washer for anti-loosening the attaching bolt and the bolt head of the attaching bolt; and an attaching bolt insertion opening formed in the road surface friction measuring rubber attached strip; characterised in that: the attaching bolt insertion opening has a shape formed by overlapping circles of different diameter sizes, a diameter of a large-diameter circular part is set larger than a diameter of a bolt head of the attaching bolt and a diameter of a small-diameter circular part is set smaller than the diameter of the bolt head of the attaching bolt and larger than a diameter of a bolt shaft; and a rubber attached strip fall prevention washer is interposed between the attaching bolt anti-loosening spring washer and the bolt head of the attaching bolt, the rubber attached strip fall prevention washer is formed into an annular shape, a notch is formed therein and a plurality of projections which project outward in a radius direction are formed thereon, an opening size of said notch is set smaller than an outer diameter of the shaft of the attaching bolt and a maximum distance between leading ends of the projections is set larger than the diameter of the large-diameter circular part in the attaching bolt insertion opening formed in the road surface friction measuring rubber attached strip, and the notch in the rubber attached strip fall prevention washer can be manually forced open by elastic deformation to allow the bolt shaft of the attaching bolt to be inserted into the forced-open notch, after which the size of the opening of the notch will return to a state where it is smaller than the diameter size of the bolt shaft. the attaching bolt insertion opening has a shape formed by overlapping circles of different diameter sizes, a diameter of a large-diameter circular part is set larger than a diameter of a bolt head of the attaching bolt and a diameter of a small-diameter circular part is set smaller than the diameter of the bolt head of the attaching bolt and larger than a diameter of a bolt shaft; and a rubber attached strip fall prevention washer is interposed between the attaching bolt anti-loosening spring washer and the bolt head of the attaching bolt, the rubber attached strip fall prevention washer is formed into an annular shape, a notch is formed therein and a plurality of projections which project outward in a radius direction are formed thereon, an opening size of said notch is set smaller than an outer diameter of the shaft of the attaching bolt and a maximum distance between leading ends of the projections is set larger than the diameter of the large-diameter circular part in the attaching bolt insertion opening formed in the road surface friction measuring rubber attached strip, and the notch in the rubber attached strip fall prevention washer can be manually forced open by elastic deformation to allow the bolt shaft of the attaching bolt to be inserted into the forced-open notch, after which the size of the opening of the notch will return to a state where it is smaller than the diameter size of the bolt shaft.