A power transmission device includes an annular transmission unit having an annular first magnetic core and a transmission coil and an annular reception unit having an annular second magnetic core and a reception coil. The transmission unit and the reception unit are arranged to face each other. The power transmission device transmits power from the transmission unit to the reception unit. The transmission unit and the reception unit are relatively rotatable about a rotation axis passing through a cavity inside the transmission unit and a cavity inside the reception unit, the first magnetic core has a structure divided into a plurality of first split cores in a circumferential direction, and the second magnetic core has a structure divided into a plurality of second split cores in the circumferential direction.