A magnetic recording medium reading device comprising: an insertion port in which a magnetic recording medium is to be inserted; a magnetic stripe detecting unit including a magnetic head that detects a magnetic stripe of the magnetic recording medium; a magnetic field generating unit that generates an interfering magnetic field to disturb reading of data recorded in the magnetic stripe of the magnetic recording medium; and a control unit that determines the existence of data recorded in the magnetic stripe based on a detection signal output from the magnetic stripe detecting unit,wherein the magnetic field generating unit is provided near the insertion port and makes the interfering magnetic field acted on the magnetic head while changing the interfering magnetic field only for a specific period to a state different from that in the other period, and characterised in that: in the case where the magnetic field generating unit generates an interfering magnetic field and the magnetic recording medium is inserted through the insertion port, the magnetic stripe detecting unit, in the specific period, reads a very small part of the data in the magnetic stripe by the magnetic head and outputs a detection signal by which the data recorded in the magnetic stripe can not be completely reproduced but only determination of the existence of data recorded in the magnetic stripe can be performed, wherein the specific period is a pause period in which the interfering magnetic field pauses. an insertion port in which a magnetic recording medium is to be inserted; a magnetic stripe detecting unit including a magnetic head that detects a magnetic stripe of the magnetic recording medium; a magnetic field generating unit that generates an interfering magnetic field to disturb reading of data recorded in the magnetic stripe of the magnetic recording medium; and a control unit that determines the existence of data recorded in the magnetic stripe based on a detection signal output from the magnetic stripe detecting unit,wherein the magnetic field generating unit is provided near the insertion port and makes the interfering magnetic field acted on the magnetic head while changing the interfering magnetic field only for a specific period to a state different from that in the other period, and characterised in that: in the case where the magnetic field generating unit generates an interfering magnetic field and the magnetic recording medium is inserted through the insertion port, the magnetic stripe detecting unit, in the specific period, reads a very small part of the data in the magnetic stripe by the magnetic head and outputs a detection signal by which the data recorded in the magnetic stripe can not be completely reproduced but only determination of the existence of data recorded in the magnetic stripe can be performed, wherein the specific period is a pause period in which the interfering magnetic field pauses. in the case where the magnetic field generating unit generates an interfering magnetic field and the magnetic recording medium is inserted through the insertion port, the magnetic stripe detecting unit, in the specific period, reads a very small part of the data in the magnetic stripe by the magnetic head and outputs a detection signal by which the data recorded in the magnetic stripe can not be completely reproduced but only determination of the existence of data recorded in the magnetic stripe can be performed, wherein the specific period is a pause period in which the interfering magnetic field pauses.