To provide a recording medium wherein it can be detected whether data are rewritten.

In a magnetic tape 10C (a recording medium) provided with a supporting body 14A, a rewritable magnetic layer 11A and a write-once type back coat layer 15B (an optical recording layer) with a dyestuff both of which are formed on the supporting body 14A, the magnetic layer 11A, the supporting body 14A and the back coat layer 15B are layered in this order.