a system for driving a semiconductor laser which is especially adapted for use with an optical recording and reproducing device is disclosed . in the write mode the power of laser light emitted from the semiconductor laser is so raised above a threshold or critical level that the laser beam focused on the surface of a recording medium can cause physical , chemical or electromagnetical changes thereof , but in the readout or reproduction mode , the power of laser light is lowered than the threshold or critical level and focused on the recording medium . a laser light power control loop is provided which is enabled or energized only in the readout or reproduction mode , so that the laser light can be maintained at a predetermined level . on the other hand , this control loop is disabled in the write or recording mode so that a predetermined value of current is superposed on the readout current sampled and held immediately before the write or recording mode is initiated and the current thus superposed flows into the semiconductor laser , whereby the power of laser light can be rapidly raised from the readout or reproducing laser light power to the write or recording laser light power .