The present invention discloses a magnetic rotary disc, which mainly comprises a metal rotary body and a plurality of magnetic elements. The metal rotary body is formed of metal iron, the magnetic elements are arranged on peripheral edge of the metal rotary body in a uniform distribution. Each magnetic element comprises a first magnetic pole portion and a second magnetic pole portion. All of the first magnetic pole portions and the second magnetic pole portions respectively belong to upper portion and lower portion of the magnetic elements. Most particularly, in all magnetic elements, the lower side of the second magnetic pole portion of any magnetic elements and the upper side of the first magnetic pole portion of the other magnetic elements partially attract each other, so that only the magnetic force lines of the first magnetic pole portions are retained outside the peripheral edge of the metal rotary body.