A disclosed secondary battery protection semiconductor device protects the secondary battery by detecting values of at least plural detection items corresponding to the secondary battery including the detection items of overcharge, overdischarge, charge overcurrent, discharge overcurrent, short-circuit current, and overheat; comparing the detected values with corresponding detection levels that are determined beforehand for each of the detection items; and based on the comparison results, turning on/off a discharge control transistor and a charge control transistor that are series-connected to the secondary battery. Among the plural detection items, a first value of a first detection item is detected, and a detection level of a second detection item is changed in accordance with the first value.