Apparatus for stabilizing carrier-envelope phase (CEP) of laser pulse generated by mode locked pulsed laser based on direct locking method includes laser oscillator, interferometer, detector and double feedback circuit. The laser oscillator includes the mode locked pulsed laser generating the laser pulse. The interferometer generates laser pulses having first and second frequency components from the laser pulse generated by the mode locked pulsed laser to generate first and second interference signals that substantially correspond to each other in time domain and space domain. The detector receives the first and second interference signals to output third and fourth interference signals by inverting phase of the second interference signal. The double feedback circuit controls the laser oscillator so that the CEP of the laser pulse generated by the mode locked pulsed laser has substantially constant value with respect to time using CEP signal obtained from the third and fourth interference signals.