A modulation circuit is provided that generates an output signal obtained by modulating an input signal with a local signal and includes a local input section that receives the local signal and generates the local signal and an inverted local signal obtained by inverting the local signal, a signal input section that receives the input signal and generates the input signal and an inverted input signal obtained by inverting the input signal, a first multiplying section that outputs from a terminal that receives the input signal a first multiplied signal obtained by multiplying the local signal with the input signal, a second multiplying section that outputs from a terminal that receives the inverted input signal a second multiplied signal obtained by multiplying the inverted local signal with the inverted input signal, an output section that adds the first multiplied signal to the second multiplied signal and generates the output signal, and a transmission line that sends to the output section the first multiplied signal output by the first multiplying section and the second multiplied signal output by the second multiplying section and has an electrical length according to a predetermined frequency as the frequency of the input signal.