A novel device for generating femtosecond double pulses is constructed, which mainly consists of three Dammann reflection gratings. Being free from transmission elements, pulse distortion is avoided. Measuring the generated double pulses with a home-made second-harmonic generation frequency-resolved optical gating, experimental results demonstrated that this device can generate double pulses exactly equal in pulse intensity and pulse width with arbitrary delay time. This method should be highly interesting for double pulses generation and its practical applications.