To achieve a reduction in the amount of coding taken in the use of an asymmetric partition and to implement efficient encoding/decoding processes exploiting the characteristics of the asymmetric partition. An image decoding device includes a motion compensation parameter derivation unit configured to derive a motion compensation parameter indicating either a uni-prediction scheme or a bi-prediction scheme. In a case that a prediction unit has a size less than or equal to a predetermined value, the motion compensation parameter derivation unit is configured to derive the motion compensation parameter by switching between the prediction schemes.