A non-contact obstacle detection system utilizing ultra sensitive capacitive techniques. Controlling the dimensions of the third electrode portion 15a constituting the high impedance portion makes it possible easily to adjust the capacitance of the electrostatic capacitor formed between the first electrode portion 12 and the third electrode portion in accordance with the load. Transaction data is continuously transmitted and received through the remaining carriers while scanning the neighbor base stations by using the primary carrier or the secondary carrier without interruption.