An object of the invention is to reduce 1/f noise and white noise at the same time by integrally reducing noise of an MR sensor and noise of an operation circuit part. A magnetoresistive sensor according to the invention includes a plurality of magnetoresistive sensor parts each having a bridge circuit in which four magnetoresistive elements are connected, and outputs of the respective magnetoresistive sensor parts are connected in parallel to one another to an input of an amplifier circuit (see FIG. 2).