Provided is a detection circuit that has a first inductor connected to two opened input ends and detects an external signal having a waveform with a gradient at each input end. The detection sensor further includes an output circuit that has a second inductor magnetically coupled with the first inductor as a primary side. In the output circuit, a third inductor constituting a delay circuit having one end connected to an intermediate tap of the second inductor is connected. Diodes are respectively connected to terminals of the second inductor in a forward direction. Other terminals of the diodes are connected to another terminal of the third inductor via elements each having an impedance characteristic. The output circuit outputs a detection signal detected at the input ends, from the other terminal(s) of at least one of the diodes.