An object of the present invention is to provide an economical and highly operable blanket mounting apparatus in which the width of a cylinder gap on a blanket cylinder is further decreased to eliminate a printing trouble such as shock-streak and to shorten the non printing length. To achieve this object, a flat bar 15a, 15b is installed at each end of a blanket 2, a notch 16 with the same size as that of the leading edge flat bar 15a is formed in a cylinder gap 3, the leading edge flat bar 15a of the blanket 2 is inserted along a leading edge opening 3a of the notch 16, and a tail edge 2b of the blanket 2 to which a flat bar 15b is fixed is reeled by a reel bar 14, by which the cylinder gap opening is blocked by the leading edge flat bar 15a.