A magnetic sensor system includes a magnetic device and a signal processing circuit. The device generates first to third detection signals corresponding to components in three directions of a magnetic field generated by a magnetic field generator that is able to change its relative position with respect to the device. The circuit includes a longest segment extraction section and a midpoint coordinate computing section. With coordinates that represent a set of values of the first to third detection signals at a certain timing in an orthogonal coordinate system being taken as a measurement point, the longest segment extraction section extracts a first point and a second point that define a line segment having the greatest length among a plurality of measurement points at a plurality of timings. The midpoint coordinate computing section determines coordinates of a midpoint of the line segment defined by the first and second points.