We demonstrate experimentally the short pulse amplitude squeezed light from a singly resonant synchronously pumped optical parametric oscillator (SPOPO). The SPOPO operates in the frequency degenerate case and below threshold, with using a periodically poled potassium titanyl phosphate crystal. The pump laser is the second harmonic of a ultrashort mode-locked femtosecond pulse at 850 nm. The reduction of quantum noise of 2.58 dB is obtained experimentally. The squeezing extent is deduced to be 4.48 dB.