PURPOSE: To provide a magnetic sensor which can be driven with a lower power source voltage while making output of a magnetic resistance element set hard to exceed an in-phase input range of an amplifying means.

CONSTITUTION: This magnetic sensor is provided with a magnetic resistance element set 2 for detecting a magnetic field change of magnetic recording medium and an amplifying means 1 for amplifying an electric signal outputted from the magnetic resistance element set 2. The amplifying means 1 is directly connected to a power source Vcc, while a resistance means R1 for feeding a voltage lower than the amplifying means 1 to the magnetic resistance element set 2 is inserted between the power source Vcc and the magnetic resistance element set 2. Resistance value of the resistance means R1 is within a range of 0.7 to 1.4 times of that of the magnetic resistance element set 2 at the time of non-magnetic field.