A compression depth calculating device (1000) including: an acceleration sensor (13)； a magnetic sensor (19)； a first calculation section (233A) which obtains a correlation； and a second calculation section (233B) which calculates a compression depth Dr of a compression operation performed after the correlation (R) has been calculated, based on a coil-to-coil distance AD acquired from the magnetic sensor (19) and the correlation (R), when the compression operation is performed after the correlation has been calculated.
