  We revisit a two-component inflaton model with a turning trajectory in the
field space, where the field slowly rolls down along the trajectory. We
consider the case when the effective mass in the direction perpendicular to the
trajectory, namely the isocurvature direction, is either of the same order as
or much larger than the Hubble parameter. Assuming that the turning angular
velocity is small, we compute analytically the corrections to the power
spectrum of curvature perturbation caused by the mediation of the heavy
isocurvature perturbation, and compare our analytic results with the numerical
ones. Especially, when M_{eff}^2>>H^2, we find that it is proportional to
M_{eff}^{-2}. This result is consistent with the one obtained previously by an
effective field theory approach.
