To provide a switch which is small-sized, light-weight, and which has high reliability.

A shape memory polymer 12 to extend in a state at molding by heating is installed in a case 11, and the bottom end is fixed and retained, and a heater 13 is arranged at the circumference. Into a hollow of the shape memory polymer 12, a lead wire 17a is inserted and penetrated from the outside, and when the shape memory polymer 12 is compressed, the upper end of the lead wire is made to protrude by a predetermined length from the shape memory polymer 12, and fixed. A contacting electrode 15, installed at one end of a flexible substrate 14, is positioned so as to oppose to a tip of the lead wire 17a. A spring 16 is installed between an upper side of the tip of the flexible substrate 14 and the case 11, and this is constituted so that in the state in which the shape memory polymer 12 is compressed, the contacting electrode 15 is pressure contacted to the lead wire 17a, and so that in the state that the shape memory polymer 12 is extended, it pushes up the contacting electrode 15 to be separated from the lead wire 17a against the elastic force of the spring 16.