An electrostatic capacitance tilt angle sensor having a size that is reduced without lowering detection capacity. The sensor is provided with a case including a first wall and a second wall facing each other. A common electrode is arranged on the first wall and a differential electrode is arranged on the second wall. A liquid electrostatic capacitance medium is accommodated in the case and contacts the common electrode and the differential electrode. The electrostatic capacitance medium includes an insulative liquid base and fine particles mixed in the base. The fine particles have a dielectric constant that is higher than that of the base.