To provide a fingerprint sensor of a structure not destroying a switching element or the like even when static electricity is discharged between a finger and a sensing pad electrode.

This device is provided with the switching element Tr formed on a semiconductor substrate (or a semiconductor layer supported by a substrate) 2, and the sensing pad electrode SP connected to one impurity area 6b of it for inducing electric charges for an amount corresponding to a capacitance value between a detection object (finger) and the electrode or supplying them through the switching element Tr. A protective means connected to the sensing pad electrode SP for releasing excessive electric charges impressed or stored on the sensing pad electrode SP, a protective diode Di for instance, is formed on the semiconductor substrate 2.