A filter adjusting circuit, has: a filter circuit which has a circuit configuration operating as an n-th order filter including n (n≧1) integrators and can switch a connection of the circuit configuration to operate as a circuit equivalent to the n integrators; a signal generating circuit that outputs a first signal having a predetermined reference frequency to the filter circuit, and outputs a second signal having the reference frequency; a phase comparator that compares a phase of a third signal and a phase of the second signal and determines a phase shift between the signals, the third signal being obtained by processing the first signal in the filter circuit and outputted from the filter circuit; and a control circuit controls the filter circuit.