An adapter of the present invention is used to connect between a lead terminal of an electronic component and a contact of a connecting device. The adapter includes a first connecting part, adapted for electrical and mechanical connection to the lead terminal; a second connecting part, disposed at a spaced relation to the first connecting part in a length direction of the electronic component and connectable to the contact electrically and mechanically; and an elastically deforming part, provided between the first and second connecting parts and elastically deformable in accordance with thermal expansion deformation or thermal contraction deformation in the length direction of the electronic component.