Abstract: The present invention realizes a highly reliable relay with a longer service life, no moving parts and no insufficient contact, being composed of a fluid path formed on an insulating member, a cell or cells formed at one end or both ends of this fluid path, a plurality of electrodes arranged along the above mentioned fluid path, a gas enclosed in the cell or cells expanding by heating and contracting by cooling, heating or cooling means located in the above cell or cells, and conductive fluid enclosed in the above fluid path; by designing so that at least the above two electrodes are arranged with one end of them in contact with conductive fluid metal enclosed in the above fluid path and one end of them contacts or does not contact with conductive fluid moving in the above fluid path due to the above gas expansion or contraction based on turning ON or OFF of the above heating or cooling means.