In order to obtain a stable signal in the higher frequency range, second harmonic oscillators injection-locked subharmonically have been investigated. The oscillator had the optimum load impedance for second harmonic generation at both the fundamental frequency and the second harmonic frequency so that high harmonic output wave could be obtained with the frequency around 17GHz. By experiments on the oscillator injection-locked subharmonically with factor of 1/2 , the stabilization of the oscillation frequency and the degradation of the phase noise were confirmed. The measurements of the locking bandwidth with the injection power level showed that the bandwidth increases with decreasing the subharmonic factor.