Handover control method, mobile station device, and base station device

A handover control method for a mobile station device whereby a determination is made regarding whether a mobile station device is in the service area of a CSG cell. When it is determined that the mobile station device is in the service area of a CSG cell, a determination is made regarding whether the CSG cell is a HPLMN. When it is determined that the CSG cell is a HPLMN and the mobile station device is set to perform measurement of neighboring cells, measurement of the neighboring cells is performed, and then the handover is carried out. Furthermore, when it is determined that the CSG cell is not a HPLMN, measurement of the neighboring cells is not performed even when the mobile station device has been set to perform measurement of the neighboring cells.