The invention relates to a device for measuring a clearance of a differential mechanism, in particular to a chip selecting machine for measuring a half axle gear clearance of the differential mechanism. Two sides in a body are provided with a first cylinder and a second cylinder respectively; output shafts of the two cylinders are connected with a first reciprocating sliding support and a second reciprocating sliding support respectively; a first shaft sleeve and a second shaft sleeve capable of reciprocating oppositely are arranged in the two sliding supports; a spline shaft and a driven shaft are arranged in the two shaft sleeves respectively; a driving device is connected to the spline shaft; the two sliding supports are provided with a third cylinder and a fourth cylinder for driving the two shaft sleeves, the spline shaft and the driven shaft to reciprocate; a seventh cylinder and an eighth cylinder are arranged on the lower rear side of the differential mechanism between the spline shaft and the driven shaft, and the output shafts of the two cylinders are connected with reciprocating measuring heads; a fifth cylinder and a sixth cylinder are arranged in the body and are provided with a clamping paw of a clamping differential mechanism respectively; and the two sides of the body are provided with a linear displacement sensor respectively. The chip selecting machine has the advantages of accurate measurement, high degree of automation, low running cost, convenient operation and the like.