A brush holder assembly comprising: a brush holder formed in a disk shape by molding of insulating resin, and including a pair of box fixing sections each including a groove formed from an outer peripheral side toward inside; and brush box assemblies each having a brush box which houses a brush therein, each of the brush box assemblies being disposed in the groove in the box fixing section, wherein the brush box assembly is formed of box-like metal, and has a plurality of mounting legs, each of the box fixing sections of the brush holder has a pair of fixing wall sections, the groove formed to be sandwiched between the fixing wall sections, and a plurality of mounting holes, and the mounting legs are inserted into the respective mounting holes, and the brush box assemblies are fixed, wherein each of the brush box assemblies includes: the brush; a brush spring for pressing the brush; characterized in that each of the brush box assemblies further includes: a metal cover plate formed with the plurality of mounting legs and disposed on one side surface of a sliding section of the brush, and covering the groove of the box fixing section; and a metal brush case having a U-shaped cross-section, and housing the brush; and wherein the cover plate is fixed to the metal brush case; wherein the metal brush case of each of the brush box assemblies faces the brush holder through gaps in a noncontact manner. a brush holder formed in a disk shape by molding of insulating resin, and including a pair of box fixing sections each including a groove formed from an outer peripheral side toward inside; and brush box assemblies each having a brush box which houses a brush therein, each of the brush box assemblies being disposed in the groove in the box fixing section, wherein the brush box assembly is formed of box-like metal, and has a plurality of mounting legs, each of the box fixing sections of the brush holder has a pair of fixing wall sections, the groove formed to be sandwiched between the fixing wall sections, and a plurality of mounting holes, and the mounting legs are inserted into the respective mounting holes, and the brush box assemblies are fixed, wherein each of the brush box assemblies includes: the brush; a brush spring for pressing the brush; the brush; a brush spring for pressing the brush; characterized in that each of the brush box assemblies further includes: a metal cover plate formed with the plurality of mounting legs and disposed on one side surface of a sliding section of the brush, and covering the groove of the box fixing section; and a metal brush case having a U-shaped cross-section, and housing the brush; and wherein the cover plate is fixed to the metal brush case; wherein the metal brush case of each of the brush box assemblies faces the brush holder through gaps in a noncontact manner. a metal cover plate formed with the plurality of mounting legs and disposed on one side surface of a sliding section of the brush, and covering the groove of the box fixing section; and a metal brush case having a U-shaped cross-section, and housing the brush; and wherein the cover plate is fixed to the metal brush case; wherein the metal brush case of each of the brush box assemblies faces the brush holder through gaps in a noncontact manner.