  The lifetimes of charmed mesons have been measured using 2.75fb$^{-1}$ of
data collected with the Belle detector at KEKB. Each candidate is fully
reconstructed to identify the flavor of the charmed meson. The lifetimes are
measured to be $\tau(D^0)=(414.8\pm3.8\pm3.4)$ fs,
$\tau(D^+)=(1040^{+23}_{-22}\pm18)$ fs and
$\tau(D_s^+)=(479^{+17}_{-16}{}^{+6}_{-8})$ fs, where the first error is
statistical and the second error is systematic. The mixing parameter $y_{CP}$
is also measured through the lifetime difference of $D^0$ mesons decaying into
CP-mixed states and CP eigenstates. We find
$y_{CP}=(1.0^{+3.8}_{-3.5}{}^{+1.1}_{-2.1})%$, corresponding to a 95%
confidence interval $-7.0%<\ycp<8.7%$.
