A safety detection alarm device for a ladder includes a control alarm unit and a sensor unit. A load sensor module, a voltage detection sensor module or an angle detection sensor module of the sensor unit is installed on the ladder. The load sensor module of the sensor unit is to detect the weight of the load. The voltage detection sensor module is to detect and sense the load of the electricity and current. The angle detection sensor module is to detect the angle of the ladder. A light alarm module or a sound alarm module is used to send an alarm to warn the user that the load, electricity or current of the ladder is over or the ladder is unstable. The present invention is safe for use and provides a better function for use.