The present invention improves the environment resistance performance of a magnetic card reader, and also improves the operation stability of a system including a higher-level device. Specifically to describe, the magnetic card reader 1, for reading magnetic data recorded in a card 4 by using a magnetic head 5, includes: a storage section (a part of a RAM 104) for storing the magnetic data read and acquired by using the magnetic head 5; a first comparing section for comparing the total number of data in the magnetic data with a prescribed first threshold; and a first judgment section for judging that the magnetic data is effective data when the total number of data in the magnetic data is less than or equal to the prescribed first threshold in the first comparing section.