A wetting sensor includes a stretchable circuit board having stretchability, a first stretchable wiring line as a wiring line formed on a main surface of the stretchable circuit board and having stretchability on the main surface, a second stretchable wiring line as a wiring line formed on the main surface of the stretchable circuit board and having stretchability on the main surface, a first electrode connected to the first stretchable wiring line, a second electrode connected to the second stretchable wiring line, a water absorbing member configured to cover at least a part of each of the first electrode and the second electrode, and a measurer configured to measure an electric characteristic between the first electrode and the second electrode which are contacting the water absorbing member.