A radio-frequency power amplifier for preventing a final-stage HBT from being destroyed is provided. An e-mail sending unit sends an e-mail sent addressed to the alternative mail address of the user to the actual mail address of the user, after setting a predetermined destination as a destination of a notice of failed delivery, if caused, of the e-mail. The water-insoluble matrix contains a crosslinked ethylene-vinyl acetate copolymer andor a crosslinked 1,2-polybutadiene and each of these is contained by a prescribed amount against the total of the water-insoluble matrix. The apparatus suppresses the output fluctuation of the motor. The cylinder can be hollow and in fixed location for causing water movements through the cylinder, or the cylinder can move through the water relative to a fixed transducer.