PURPOSE: To verify with information whether or not a regular card is obtained and to effectively prevent the forge of the card by providing an area to record the verifying information by the function of value information and arbitrary information at the recording area of a magnetic card.
CONSTITUTION: On the surface of a recording and producing magnetic layer 2 provided on a magnetic card substrate 1, a general information area 5 to record value information A and an arbitrary information area 4 to record arbitrary information B with an irregularly changing recording density are provided. Further, a verifying information area 6 to record, as verifying information C, the value of a function F(A,B) with the value information A and the arbitrary information B as a variable is provided. The arbitrary information B is recorded with the recording density of a pattern read irregularly out of plural patterns of the recording density to change together with the time specified beforehand by the magnetic layer 2. The length of the arbitrary recording area 4 is determined and recorded so as to be different according to an individual magnetic card based on random numbers.