A pinion shaft support device having a double row ball bearing comprising: an outer ring that has double row raceway surfaces (12a, 12b) having diameters different from each other; an inner ring that has double row raceway surfaces (13a, 13b) that correspond to the double row raceway surfaces (12a, 12b) of the outer ring; a plurality of small-diameter-side balls and a plurality of large-diameter-side balls that are arranged between the double row raceway surfaces (12a, 12b) of the outer ring and the double row raceway surfaces (13a, 13b) of the inner ring with different pitch diameters of ball sets, and an inward protruding portion that extends further radially inward than an axially outer end of a small-diameter-side raceway surface among the double row raceway surfaces (12a, 12b) of the outer ring is formed on a small-diameter-side end portion of the outer ring so as not to contact the small-diameter-side balls, wherein, in said pinion shaft support device, the said outer ring of the double row ball bearing is fitted to a housing and a small-diameter-side end face of the outer ring is received by an outer ring receiving portion formed in the housing, and the said inner ring of the double row ball bearing is fitted to a pinion shaft and a large-diameter-side end face of the inner ring is received by an inner ring receiving portion formed in the pinion shaft, wherein the inward protruding portion extends further radially inward than an inner periphery of the outer ring receiving portion of the housing, characterized in that a small-diameter-side end face of the outer ring is formed as a ground surface, and an axially outer face of the inward protruding portion is formed as a turned surface located axially inward of the small-diameter-side end face of the outer ring, and the axially outer face of the inward protruding portion is disposed so as not to overlap with the small-diameter-side raceway surface of the outer ring in the axial direction. an outer ring that has double row raceway surfaces (12a, 12b) having diameters different from each other; an inner ring that has double row raceway surfaces (13a, 13b) that correspond to the double row raceway surfaces (12a, 12b) of the outer ring; a plurality of small-diameter-side balls and a plurality of large-diameter-side balls that are arranged between the double row raceway surfaces (12a, 12b) of the outer ring and the double row raceway surfaces (13a, 13b) of the inner ring with different pitch diameters of ball sets, and an inward protruding portion that extends further radially inward than an axially outer end of a small-diameter-side raceway surface among the double row raceway surfaces (12a, 12b) of the outer ring is formed on a small-diameter-side end portion of the outer ring so as not to contact the small-diameter-side balls, wherein, in said pinion shaft support device, the said outer ring of the double row ball bearing is fitted to a housing and a small-diameter-side end face of the outer ring is received by an outer ring receiving portion formed in the housing, and the said inner ring of the double row ball bearing is fitted to a pinion shaft and a large-diameter-side end face of the inner ring is received by an inner ring receiving portion formed in the pinion shaft, wherein the inward protruding portion extends further radially inward than an inner periphery of the outer ring receiving portion of the housing, characterized in that a small-diameter-side end face of the outer ring is formed as a ground surface, and an axially outer face of the inward protruding portion is formed as a turned surface located axially inward of the small-diameter-side end face of the outer ring, and the axially outer face of the inward protruding portion is disposed so as not to overlap with the small-diameter-side raceway surface of the outer ring in the axial direction.