Polymer electrolyte, electrochemical device, and actuator element

A polymer electrolyte which comprises an ionic liquid (A) and a block copolymer (B) as essential ingredients, which block copolymer (B) comprises one or more of polymer block(s) (P) being compatible with (A) and one or more of polymer block(s) (Q) being incompatible with (A). (A) and (P) mutually dissolve each other to form one phase (X), and (Q) forms a phase (Y) being incompatible with phase (X), and phase (X) and phase (Y) are mutually micro phase separated. The polymer electrolyte of the present invention shows practical ion conductivity, is excellent in retention of ionic liquid, and moreover, is also excellent in heat resistance and mechanical strength. Furthermore, the electrochemical device and actuator element of the invention are swiftly displaced in accordance with application of a voltage, and can be actuated stably for a long period due to the liquid-retaining property and mechanical strength of the polymer electrolyte used, and, therefore, can suitably be used in the fields of medical instruments, micro-machines, industrial robot, personal robot, etc.