These days, we have many opportunities to launch small satellites as a piggyback payload. Faced with this situation, in this study, we deal with 3-axis attitude control of a small satellite equipped with a DGVSCMG (Double-Gimbal Variable-Speed Control Moment Gyro). Unlike conventional single-gimbal CMGs, only one DGVSCMG can attain 3-axis attitude control. This saves an inner space of a satellite and reserves an extra space for other missions. Satellite dynamics is described by a nonlinear differential equation. To avoid difficulties coming from this nonlinearity, we modeled its dynamics as an LPV (Linear Parameter-Varying) system and applied a GS (Gain-Scheduled) controller to this model. Compared with a conventional method, it is shown that the control performance has been improved.