Biomagnetic field measurement is a promising tool for the investigation of electrical activities in a living body. Room temperature (RT) magnetic sensors with an improved resolution such as magnetoresistance (MR) devices have been recently employed for the detection of weak magnetic fields, which were earlier detected solely using superconducting interference device magnetic sensors. The position, orientation, and sensitivity of each magnetic sensor in a sensor array must be precisely determined for accurate magnetic source analysis. We proposed a calibration method using an array of multiple coils, which is applicable to an RT magnetic sensor array. To demonstrate the validity of the proposed calibration method, we applied it to an MR device-based magnetocardiography (MCG) system equipped with an L-shaped planar sensor array, which was newly developed for the simultaneous observation of both anterior and lateral sides of the body. The deviation of the sensor parameters from the designed values was estimated via calibration. The result of the marker coil localization test indicated that the calibration considerably improved the accuracy of the magnetic source analysis. Finally, we demonstrated a preliminary MCG measurement using the calibrated magnetic sensor array.