The shear stress σ and normal stress differenceν3,the sum of the first and the second normal stress differences, were measured for a concentrated polystyrene solution in double‐step shear deformations: a shear strainγ1was applied at timet=−t1,another shear strainγ2was added att=0,and the stresses were measured fort>0.Whent1andtwere larger than a certain characteristic timeτk,the observed results for σ andν3were in accord with the prediction of the tube‐model theory of Doi and Edwards for various combinations ofγ1andγ2.Here the characteristic timeτk,previously determined from the strain‐dependent relaxation modulus, gives the measure of the equilibration time of the contour length of polymer chain. The results fort>τk≫t1were well described with the phenomenological BKZ model. The success of this model fort>τk≫t1can be accounted for with the concept of tube model.