A 12-stage secondary-electron multiplier with CuBe alloy(2% Be)dynodes was constructed. The dynodes were treated and polished by the same method as previously reported. The over-all gain of this multiplier, when installed in a mass spectrometer, settled down to about 10⁴, the applied voltage being 300 volts per stage and the ion energy about 5.6KV. The noise level, measured with the vibrating reed electrometer, corresponds to the ion current of about1.5×10^-18A at the pressure of 1.4×10^-5mmHg. The over-all gain is nearly constant in the pressure region of -10^-5mmHg, and is not seriously affected by exposure for a short time.