  The formation of a circumstellar disk in collapsing cloud cores is
investigated with three-dimensional magnetohydrodynamic simulations. We prepare
four types of initial cloud having different density profiles and calculate
their evolution with or without a sink. To investigate the effect of magnetic
dissipation on disk formation, the Ohmic dissipation is considered in some
models. Calculations show that disk formation is very sensitive to both the
initial cloud configuration and the sink treatment. The disk size considerably
differs in clouds with different density profiles even when the initial clouds
have almost the same mass-to-flux ratio. Only a very small disk (\sim 10 AU in
size) appears in clouds with a uniform density profile, whereas a large disk
(\sim 100 AU in size) forms in clouds with a Bonnor-Ebert density profile. In
addition, a large sink accretion radius numerically impedes disk formation
during the main accretion phase and tends to foster the misleading notion that
disk formation is completely suppressed by magnetic braking. The protostellar
outflow is also greatly affected by the sink properties. A sink accretion
radius of \lesssim 1 AU and sink threshold density of \gtrsim 10^ 13 cm^-3 are
necessary for investigating disk formation during the main accretion phase.
