  Let $d\geq 2$ be an integer and let $\omega_1,\cdots ,\omega_d$ be moduli of
continuity in a specified class which contains the moduli of H\"{o}lder
continuity. Let $f_k$, $k\in\{1,\cdots,d\}$, be $C^{1+\omega_k}$ orientation
preserving diffeomorphisms of the circle and $f_1,\cdots, f_d$ commute with
each other. We prove that if the rotation numbers of $f_k$'s are independent
over the rationals and $\omega_1(t)\cdots\omega_d(t)=t\omega(t)$ with
$\lim_{t\rightarrow 0^+}\omega(t)=0$, then $f_1,\cdots,f_d$ are simultaneously
(topologically) conjugate to rigid rotations.
