Shear-thickening phenomena observed in thermo-reversible gels of telechelic associating polymers are theoretically studied on the basis of the transient network model. Non-linear tension due to over-stretching of the middle chain leads to thickening, if the coupling constant g of the end-chain dissociation rate to the middle chain tension fulfills a certain condition. We give the condition for thickening in terms of the molecular parameters.