1. An adaptive control device comprising: an identifier that estimates an unknown coefficient in a discrete-time transfer function model P(z) (z: delay operator) of a controlled object, based on a manipulated variable supplied to the controlled object and a controlled variable of the controlled object to the manipulated variable, to identify the discrete-time transfer function model P(z), a feedforward controller that is expressed by a discrete-time transfer function model using an inverse model 1/{circumflex over (P)}(z) of an identification model {circumflex over (P)}(z) which is resulted from identification by the identifier and that generates a feedforward manipulated variable as at least a part of the manipulated variable to an input control target value, wherein the controlled object is configured such that the discrete-time transfer function model P(z) of the controlled object is expressed by equation (i), P ( z ) = b ( z n + h n z n - 1 + … + h 2 z + h 1 ) z n + a n z n - 1 + … + a 2 z + a 1 ( i ) where b, a 1 ,. .. , a n : unknown coefficient, and h 1 ,. .. , h n : known real number, the identifier, when estimating each coefficient b, a 1 ,. .. , a n of the discrete-time transfer function model P(z) of equation (i), estimates a single unknown coefficient b of numerator in non-expanded form of the numerator.