A floppy disk in which the binder for fixing a magnetic substance in the recording layer of the magnetic disk is a polyester polyurethane and the liner of the jacket contains an acrylic fiber and in addition a fiber treating agent having a surface tension in a specific range. The floppy disk is excellent in workability, can be prepared in high yields because the number of dusts generated upon its preparation is small, and also is excellent in the permanence of recording performance.