We report the identification of the optical
counterpart to the companion of the millisecond pulsar PSR J2317+1439. At the
timing position of the pulsar, we find an object with magnitudes of
g = 22.96±0.05 mag, r = 22.86±0.04 mag and i =
22.82±0.05 mag. The magnitudes and colors of the object are consistent with
it being a white dwarf. By comparing with white dwarf cooling models, we
estimate that it has a mass of 0.39+0.13−0.10 M⊙, an effective temperature
of 8077+550−470 K and a cooling age of 10.9±0.3 Gyr. Combining our results
with published constraints on the orbital parameters obtained through pulsar
timing, we estimate the pulsar mass to be 3.4+1.4−1.1 M⊙. Although the
constraint on the pulsar mass is still weak, there is a significant possibility that the pulsar could be more massive than two solar mass.