1. A neural network type of apparatus for detecting an internal state of a secondary battery implemented in a battery system, the apparatus comprising: detecting means for detecting, in real time, electric signals indicating an operating state of the battery during a predetermined period of time, the electric signals being voltage and current of the battery; producing means for producing, using the electric signals, an input parameter required for estimating the internal state of the battery, the input parameter reflecting calibration of a present charged state of the battery and consisting of a first input parameter indicating the operating state of the battery and a second input parameter indicating a degraded state of the battery, wherein the producing means includes: means for calculating the first input parameter on the basis of data of the voltage and current of the battery, and means for calculating the second input parameter in response to a state of predetermined charge of the battery; and calculating means for calculating an output parameter indicating the charged state of the battery by processing both the first and second input parameters based on a neural network calculation technique, wherein the second input parameter calculating means includes means for calculating data of history of both the voltage and the current into an approximate expression on a least-squares methods, means for calculating a present value of an open-circuit voltage of the battery on the approximate expression, the present value being included in the first input parameters, and the output parameter calculating means is configured to calculate the output parameter by using both the first parameter consisting of the data of the voltage history, the data of the current history, and the present value of the open-circuit voltage and the second input parameter; the second input parameter indicating the degraded state of the battery is both an open-circuit voltage and an internal resistance of the battery detected in response to a state of predetermined charge of the battery, the output parameter indicating the present charged state is one of and SOC (state of charge) of the battery, an SOH (state of health) of the battery, and a function whose variables including information indicative of the SOC and SOH, and the function is a degree of degradation of the battery which is defined by an expression of: the degree of desegregation=SOH/(initial full charge capacity×SOC).