A storage box assembly, comprising: a housing comprising: a base plate; and first and second upright sidewalls at first and second side edges of the base plate, each upright sidewall having a front groove and a rear groove on a top surface thereof; a storage box arranged to be accommodated movably in the housing, the storage box having: a first side panel and second side panel opposite the first side panel, each of the first and second side panels having an upper end slanted downward from a front end toward a rear end of the storage box such that the height of the front end is greater than the height of the rear end, a bottom panel; an open top; and a front lifter and a rear lifter protruding from the upper end of each of the first and second side panels; and a cover configured to cover the open top when the storage box is in a closed position within the housing, the cover comprising: a pair of side surfaces having bottom ends which are slanted such that the height of a front end of each side surface is less than the height of a rear end of each side surface; a front lift recess and a rear lift recess arranged to receive the front lifter and rear lifter, respectively, of the storage box such that the front lifter and rear lifter are seated in the front lift recess and rear lift recess when the storage box is in the closed position; a front protrusion and a rear protrusion which protrude from each side surface and are configured to be seated in the front groove and rear groove, respectively; and a first flange and a second flange at the bottom ends of both side surfaces, wherein the front lift recess and rear lift recess are disposed on both first and second flanges, wherein a width of the rear lifter is larger than a width of the front lifter, so that the rear lifter is not received in the front lift recess, and wherein, when the storage box is withdrawn to maximum open position, the front lifters are covered by the cover by being located behind a front end of the cover. a housing comprising: a base plate; and first and second upright sidewalls at first and second side edges of the base plate, each upright sidewall having a front groove and a rear groove on a top surface thereof; a base plate; and first and second upright sidewalls at first and second side edges of the base plate, each upright sidewall having a front groove and a rear groove on a top surface thereof; a storage box arranged to be accommodated movably in the housing, the storage box having: a first side panel and second side panel opposite the first side panel, each of the first and second side panels having an upper end slanted downward from a front end toward a rear end of the storage box such that the height of the front end is greater than the height of the rear end, a bottom panel; an open top; and a front lifter and a rear lifter protruding from the upper end of each of the first and second side panels; and a first side panel and second side panel opposite the first side panel, each of the first and second side panels having an upper end slanted downward from a front end toward a rear end of the storage box such that the height of the front end is greater than the height of the rear end, a bottom panel; an open top; and a front lifter and a rear lifter protruding from the upper end of each of the first and second side panels; and a cover configured to cover the open top when the storage box is in a closed position within the housing, the cover comprising: a pair of side surfaces having bottom ends which are slanted such that the height of a front end of each side surface is less than the height of a rear end of each side surface; a front lift recess and a rear lift recess arranged to receive the front lifter and rear lifter, respectively, of the storage box such that the front lifter and rear lifter are seated in the front lift recess and rear lift recess when the storage box is in the closed position; a front protrusion and a rear protrusion which protrude from each side surface and are configured to be seated in the front groove and rear groove, respectively; and a first flange and a second flange at the bottom ends of both side surfaces, wherein the front lift recess and rear lift recess are disposed on both first and second flanges, a pair of side surfaces having bottom ends which are slanted such that the height of a front end of each side surface is less than the height of a rear end of each side surface; a front lift recess and a rear lift recess arranged to receive the front lifter and rear lifter, respectively, of the storage box such that the front lifter and rear lifter are seated in the front lift recess and rear lift recess when the storage box is in the closed position; a front protrusion and a rear protrusion which protrude from each side surface and are configured to be seated in the front groove and rear groove, respectively; and a first flange and a second flange at the bottom ends of both side surfaces, wherein the front lift recess and rear lift recess are disposed on both first and second flanges, wherein a width of the rear lifter is larger than a width of the front lifter, so that the rear lifter is not received in the front lift recess, and wherein, when the storage box is withdrawn to maximum open position, the front lifters are covered by the cover by being located behind a front end of the cover.