A nonaqueous electrolyte type lithium ion secondary battery system comprising: a voltage obtaining part for obtaining charging voltage when a charging current is applied to a nonaqueous electrolyte type lithium ion secondary battery and obtaining discharging voltage when a discharging current is generated by the nonaqueous electrolyte type lithium ion secondary battery, a respective voltage value being measured every time the current applying direction is inverted; a coefficient calculating part for calculating a coefficient BC, BD of a quadratic term of an approximated curve of a quadratic function with respect to changes in the voltage values within a previously set sampling period for each of the charging voltage and the discharging voltage obtained by the voltage obtaining part, respectively, and repeating the calculation over a plurality of the sampling periods; and a deposition determining part for determining whether or not there is a possibility of lithium deposition in the nonaqueous electrolyte type lithium ion secondary battery based on a tendency of changing with time of the coefficient of charging voltage BC and the coefficient of discharging voltage BD calculated by the coefficient calculating part, wherein the deposition determining part is arranged to determine that: there is no possibility of lithium deposition when the occurrence frequency of a symmetry phenomenon is less than a previously set threshold frequency, the symmetry phenomenon being the case where BCn < BC(n+1) and BDn > BD(n+1) or the case where BCn > BC(n+1) and BDn < BD(n+1) with "n" being the number of the sampling period, and there is a possibility of lithium deposition when the occurrence frequency of the symmetry phenomenon is as high as the threshold frequency or more. a voltage obtaining part for obtaining charging voltage when a charging current is applied to a nonaqueous electrolyte type lithium ion secondary battery and obtaining discharging voltage when a discharging current is generated by the nonaqueous electrolyte type lithium ion secondary battery, a respective voltage value being measured every time the current applying direction is inverted; a coefficient calculating part for calculating a coefficient BC, BD of a quadratic term of an approximated curve of a quadratic function with respect to changes in the voltage values within a previously set sampling period for each of the charging voltage and the discharging voltage obtained by the voltage obtaining part, respectively, and repeating the calculation over a plurality of the sampling periods; and a deposition determining part for determining whether or not there is a possibility of lithium deposition in the nonaqueous electrolyte type lithium ion secondary battery based on a tendency of changing with time of the coefficient of charging voltage BC and the coefficient of discharging voltage BD calculated by the coefficient calculating part, wherein the deposition determining part is arranged to determine that: there is no possibility of lithium deposition when the occurrence frequency of a symmetry phenomenon is less than a previously set threshold frequency, the symmetry phenomenon being the case where BCn < BC(n+1) and BDn > BD(n+1) or the case where BCn > BC(n+1) and BDn < BD(n+1) with "n" being the number of the sampling period, and there is a possibility of lithium deposition when the occurrence frequency of the symmetry phenomenon is as high as the threshold frequency or more. there is no possibility of lithium deposition when the occurrence frequency of a symmetry phenomenon is less than a previously set threshold frequency, the symmetry phenomenon being the case where BCn < BC(n+1) and BDn > BD(n+1) or the case where BCn > BC(n+1) and BDn < BD(n+1) with "n" being the number of the sampling period, and there is a possibility of lithium deposition when the occurrence frequency of the symmetry phenomenon is as high as the threshold frequency or more.