Quiver Hecke algebra is a graded algebra associated with a symmetrizable Kac-Moody algebra, and its module category provides a categorification of the quantum group. In this talk, I will explain that the subcategory corresponding to the quantum unipotent subgroup determined by an element of the Weyl group has a structure of an affine highest weight category. This result was previously proved only when Kac-Moody Lie algebra is finite-dimensional or of symmetric affine type, by Kato, Brundan, Kleshchev, McNamara and Muth. Our approach differs from these prior studies in that we explicitly construct the standard modules using determinantial modules and analyze them via distinguished homomorphisms known as R-matrices.