A sensor apparatus is provided, including: a hollow cylindrical sleeve having a first side and a second side disposed on two end openings thereof, respectively； an electrode disposed on the first side of the sleeve for measuring a signal； a conductive line electrically connected to the electrode for transmitting the signal measured by the electrode； and a siphoning portion having a suction port connected and tightly sealed with the second side of the sleeve and an outlet port for discharging gas from the sleeve, thus creating a vacuum effect to enable the electrode to be sucked to the head of a subject. Therefore, the present invention avoids the conventional drawback of discomfort of the subject caused by the use of a conductive material.
