A variable resonator that comprises a loop line (902) to which two or more switches (903) are connected and N variable reactance means (102) (N≧3), in which switches (903) are severally connected to different positions on the loop line (902), the other ends of the switches are severally connected to a ground conductor, and the switches are capable of switching electrical connection/non-connection between the ground conductor and the loop line (902), the variable reactance blocks (102) are severally settable to the same reactance value, and the variable reactance blocks (102) are electrically connected to the loop line (902) as branching circuits along the circumference direction of the loop line (902) at equal electrical length intervals.