1. A sliding mode controller applied to a controlled object system including at least one controlled object, the sliding mode controller comprising: an electronic control unit configured to control the controlled object system by an adaptive sliding mode control including a linear input term, a non-linear input term, and an adaptive term; means configured to acquire an operation state of the controlled object system; and means configured to control the operation state of the controlled object system, wherein the electronic control unit is configured to: learn the adaptive term by adding one of a value of the non-linear input term and a predetermined proportion of the value of the non-linear input term to the adaptive term when the operation state of the controlled object system changes from a transient state to a stationary state; correct the non-linear input term by subtracting the value added to the adaptive term from the non-linear input term; and control the controlled object system by the adaptive sliding mode control using the learned adaptive term and the corrected non-linear input term.