IMAGE DECODING DEVICE

There is a problem in that implicit MTS performance is lost in a case that the implict MTS is combined with secondary transform. The present invention provides an image decoding apparatus that can more preferably apply transform by MTS and secondary transform. A video decoding apparatus includes: a second transformer configured to apply transform using a transform matrix to the transform coefficient to modify the transform coefficient in a case that secondary transform is enabled; a first transformer configured to apply separate transform including vertical transform and horizontal transform to the transform coefficient; and an implicit transform configuration unit configured to disable implicit transform in a case that the secondary transform is enabled, an intra subpartition mode is not used, and subblock transform is not used, and configured to derive a horizontal transform type according to a width of a target TU and derive a vertical transform type according to a height of the target TU in a case that the implicit transform is enabled. The first transformer performs transform according to the vertical transform type, and transform according to the horizontal transform type.