A periodic-waveguide cyclotron maser is presented in this paper. In this device, a nonrelativistic electron beam undergoes a cyclotron interaction with traveling waves in an inductive periodic waveguide. Results of amplifier and oscillator experiments are presented. These experiments are conducted in the microwave regime (∼10 GHz) with low-energy (<10 keV), low-current (<1 A) electron beams. Considerable amplification (>10 dB) and rf power (∼100 W) have been measured in the amplifier and oscillator experiments, respectively.