PURPOSE: To reduce the generation rate of a reading error by inserting valid data held by first and second discrimination bits in the process of the data column of a magnetic card and reading valid data based on each discrimination bit.

CONSTITUTION: When a card insertion signal bar CLS becomes 'L' by the insertion of a card, next, signals RDT are fetched from low-order bits one bit by one bit in the shift register of a RAM 3a by the fall of a signal bar RCL and read data is detected to be a tip display bit (first discrimination bit) A1, bar RDT data is successively fetched in the RAM 3a every fall of a read clock bar RCL, that is, every detection of a bar RCL=L. When data corresponding to 21 bytes, that is, valid data D1 (20 bytes) and a rear end display bit (second discrimination bit) A2 (1 byte) are fetched, the state is judged as no error when it is detected that the 21st byte data is a rear end display dit A2.