A rear discharge type mower apparatus comprises: a blade housing having a top plate, a front wall and at least one side wall; a support shaft supported by the blade housing and extending vertically; a rotatable blade supported by the support shaft, a tip end of the blade forming a rotation path; a guide plate located rearwardly of the front wall and having a shape extending along the rotation path of a corresponding blade, and forming an opening for ejecting cut grass rearwardly, wherein the guide plate has: a first end located in an upstream position with respect to a rotating direction of the corresponding blade and located rearwardly of a corresponding support shaft and the first end defining one end of the opening, and a second end located in a downstream position with respect to the rotating direction of the corresponding blade and located rearwardly of the corresponding support shaft and the second end defining the other end of the opening; an auxiliary plate extending from an area of the first end into inside the rotation path of the corresponding blade, and having a surface for deflecting rearwardly a part of cut grass moved by a rotation of the corresponding blade, wherein a lower edge of the auxiliary plate is closer to the top plate than the corresponding blade.