1. A loop filter comprising: a register configured to store a result of arithmetic operation performed on a complex signal and outputs the stored complex signal; a first multiplier configured to multiply the complex signal output from the register and a predetermined coefficient; an absolute value judging unit configured to output a multiplier coefficient used to control such that the amplitude of the complex signal output from the register is held in a predetermined range; a multiplier configured to multiply an output from the first multiplier and the multiplier coefficient; a second multiplier configured to multiply an input signal and a value equal to 1−the predetermined coefficient; and an adder configured to add an output from the multiplier to an output from the second multiplier and input a result of addition into the register.