  We consider simultaneous and continuous measurement of two noncommutative
observables of the system whose commutator is not necessarily a $c$-number. We
revisit the Arthurs-Kelly model and generalize it to describe the simultaneous
measurement of two observables of the system. Using this generalized model, we
continuously measure the system by following the scheme proposed by Scott and
Milburn [Scott and Milburn, Phys. Rev. A 63, 042101 (2001)]. We find that the
unconditioned master equation reduces to the Lindblad form in the continuous
limit. In addition, we find that the master equation does not contain a cross
term of these two measurements. Finally, we propose a scheme to prepare the
state of a two-level system in an external field by feedback control based on
the simultaneous, continuous measurement of the two observables.
