An apparatus for detecting a state of a secondary battery having a positive electrode (60, 70) and a negative electrode (62, 72), comprising: a first detection unit using a potential of a casing of said secondary battery insulated from said positive electrode (60, 70) and said negative electrode (62, 72) as a reference potential to detect a potential difference between said reference potential and a potential of said positive electrode (60, 70) as a detected positive electrode potential difference (ΔVP); a second detection unit using said potential of said casing as a reference potential to detect a potential difference between said reference potential and a potential of said negative electrode (62, 72) as a detected negative electrode potential difference (ΔVN); a first calculation unit for calculating a state of charge of said secondary battery; a second calculation unit for calculating a normal positive electrode potential difference (ΔVP) and a normal negative electrode potential difference (ΔVN) based on said state of charge of said secondary battery, said normal positive electrode potential difference (ΔVP) indicating a potential difference between said reference potential and a potential of said positive electrode (60, 70) that is provided when said positive electrode (60, 70) is normal, said normal negative electrode potential difference (ΔVN) indicating a potential difference between said reference potential and a potential of said negative electrode (62, 72) that is provided when said negative electrode (62, 72) is normal; and an abnormality detection unit for comparing said detected positive electrode potential difference (ΔVP) with said normal positive electrode potential difference (ΔVP) and determining that said positive electrode (60, 70) is abnormal when said detected positive electrode potential difference (ΔVP) and said normal positive electrode potential difference (ΔVP) have a difference exceeding a predetermined range, and for comparing said detected negative electrode potential difference (ΔVN) with said normal negative electrode potential difference (ΔVN) and determining that said negative electrode (62, 72) is abnormal when said detected negative electrode potential difference (ΔVN) and said normal negative electrode potential difference (ΔVN) have a difference exceeding a predetermined range. a first detection unit using a potential of a casing of said secondary battery insulated from said positive electrode (60, 70) and said negative electrode (62, 72) as a reference potential to detect a potential difference between said reference potential and a potential of said positive electrode (60, 70) as a detected positive electrode potential difference (ΔVP); a second detection unit using said potential of said casing as a reference potential to detect a potential difference between said reference potential and a potential of said negative electrode (62, 72) as a detected negative electrode potential difference (ΔVN); a first calculation unit for calculating a state of charge of said secondary battery; a second calculation unit for calculating a normal positive electrode potential difference (ΔVP) and a normal negative electrode potential difference (ΔVN) based on said state of charge of said secondary battery, said normal positive electrode potential difference (ΔVP) indicating a potential difference between said reference potential and a potential of said positive electrode (60, 70) that is provided when said positive electrode (60, 70) is normal, said normal negative electrode potential difference (ΔVN) indicating a potential difference between said reference potential and a potential of said negative electrode (62, 72) that is provided when said negative electrode (62, 72) is normal; and an abnormality detection unit for comparing said detected positive electrode potential difference (ΔVP) with said normal positive electrode potential difference (ΔVP) and determining that said positive electrode (60, 70) is abnormal when said detected positive electrode potential difference (ΔVP) and said normal positive electrode potential difference (ΔVP) have a difference exceeding a predetermined range, and for comparing said detected negative electrode potential difference (ΔVN) with said normal negative electrode potential difference (ΔVN) and determining that said negative electrode (62, 72) is abnormal when said detected negative electrode potential difference (ΔVN) and said normal negative electrode potential difference (ΔVN) have a difference exceeding a predetermined range.