[ Mathematical Expression 3 ] G ( ?? ) = { 4 ?? m / L ( 0 ??? ?? m ??? 0.25 L ) - 4 ?? m / L + 2 ( 0.2 5 L < ?? m ??? 0.75 L ) 4 ?? m / L - 4 ( 0.75 L < ?? m < L ) ( Eq . 2 ) where ??m is the remainder left when ?? divided by a fundamental period L. In a case where a position detector 6 is such a device as a rotary encoder for detecting rotational positions, for example, position detection errors