To provide a cantilever sensor having high measuring accuracy and reduced in size and cost.

This sensor includes a cantilever fixed to a support part at its one end and having a flow passage formed therein, a piezoelectric element constituted by a piezoelectric body and electrode parts formed on the both sides of the piezoelectric body and disposed at least on one surface of the cantilever, a driving part applying voltage to the electrode parts of the piezoelectric element to vibrate the cantilever, a detecting part detecting vibration of the cantilever from expansion and contraction of the piezoelectric element and a liquid supplying means letting a liquid flow through the flow passage in the cantilever.