An angle detecting head provided with an emitter and a pair of receivers is rocked, and a bent surface of a workpiece bent by a punch and a die of a bending machine is irradiated with a measurement light from the emitter, a reflected light is received by the pair of receivers, and a bending angle of the workpiece is obtained from a peak value of the light received by the respective receivers. The polymer material has first and second states in which degrees of the carrier transport property are different from each other, microscopic structures in the first and second states are different from each other, and one of the first and second states can be changed into the other state. The plurality of bases comprise side supports for coupling with the first connector. The RF spectrum sensing unit measures information indicative of usage of a spectrum by other devices. Its use of a novel induced dipole coupling for rotation of planar mirrors lets it operate with greater simplicity and efficiency than other display devices. The insulative body of the igniter can be made of a ceramic.