The aim of the paper was to study the strain variation during the isothermal B2 → B19′ transformation in NiTi-based alloy. It was found that isothermal holding of the Ti_40.7Hf_9.5Ni_44.8Cu₅ alloy under a stress of 235 MPa at constant temperatures, which were close to the start temperature of the B2 → B19′ transition, was accompanied by an additional strain variation. This strain was completely reversible on further heating and depended on the position of the holding temperature compared to the start temperature of the forward transformation. The maximum of isothermal strain of 2.9% was observed during holding at a temperature of 50 °C.