A person-detecting sensor includes: a range-finding unit that decides whether a distance to a detection object falls within a predetermined detection distance range; a received-light quantity decision unit that decides whether a received-light quantity is equal to or greater than a predetermined received-light quantity threshold; and a continuation decision unit that decides whether a state of the detection object being present is ongoing. In the received-light quantity decision unit, after water discharge is started upon the detection determination unit determining a detection object to be under detection state, for a period during which the continuation decision unit decides the state in which the detection object being present is ongoing, the received-light quantity threshold is set to be lower than prior to when the water discharge is started.