A simple and robust photonic radio frequency multiplication with continuously tunable multiplication factor by using a Fabry-Pérot laser diode (FP-LD) is proposed and demonstrated. In a FP-LD, the four-wave mixing effect can create new harmonic components, and the injection-locking behavior is able to lock and amplify one of the sidebands. When the output signal beats on a high speed photodetctor, the multiplication frequencies with a factor more than 41 can be obtained. The tunability is implemented by detuning the injection wavelength. In the experimental demonstration, the frequency components around 20 GHz are generated from a 500 MHz (or 1 GHz) sinusoidal signal. The measured single sideband phase noise is −95 dBc/Hz at a 10 kHz frequency offset.