A hybrid forklift truck is provided with an engine, a battery-driven motor generator, and a battery control device that prevents excessive exhaustion or charging of the battery. The state of charge (SOC) of the battery is determined from the battery voltage and SOC when battery current is zero for at least a predetermined time period and from the battery voltage, current and SOC when discharge current is constant for at least a predetermined time period. SOC is revised whenever battery current is zero or constant for at least the predetermined time period, and SOC at any point of time in operation of the forklift truck is estimated by integrating battery current from the SOC revision and subtracting the integrated current from the revised SOC. Drive power of the engine and motor generator are allocated according to a relationship between permissible discharge and charge current and SOC of the battery.