ELECTROMAGNETICALLY-COUPLED STATE DETECTION CIRCUIT, POWER TRANSMISSION APPARATUS, CONTACTLESS POWER TRANSMISSION SYSTEM, AND ELECTROMAGNETICALLY-COUPLED STATE DETECTION METHOD

An electromagnetically-coupled state detection circuit including a detection unit that measures a primary side Q value of a circuit containing a primary side coil electromagnetically coupled with a secondary side coil and power transmission efficiency to the secondary side coil, corrects the power transmission efficiency based on the Q value of the primary side coil, and detects a state of electromagnetic coupling with the secondary side coil based on an obtained corrected value of the power transmission efficiency.