An ISG entry apparatus and method is capable of operating ISG logic without employing a battery sensor. The ISG entry apparatus includes a starting voltage detection unit detecting a starting voltage of an ISG vehicle having no battery sensor mounted therein, a cooling water detection unit detecting a cooling water temperature of the ISG vehicle, an ISG entry frequency detection unit detecting an ISG entry frequency of the ISG vehicle, an accumulated charge amount detection unit detecting an accumulated charge amount of the ISG vehicle during driving, a starting number counting unit counting the starting number of the ISG vehicle, and an engine control unit determining whether or not to enter a mode in which an ISG operation is performed based on the starting voltage, the cooling water temperature, the ISG entry frequency, the accumulated charge amount, and the starting number and performing an ISG operation.