This invention provides a communication apparatus, which suppresses abrupt changes of a current and voltage generated in a communication line upon connecting an external telephone to the communication line, and a control method thereof. To accomplish this, in a communication apparatus of this invention, when an off-hook state of an external telephone is detected upon connecting the external telephone to a communication line, an SOC captures a line using a first line capture means having an impedance lower than the external telephone side, and then switches an H-relay to connect the external telephone to the communication line. Furthermore, the SOC temporarily switches a line capture state to a second line capture means having an impedance higher than the first line capture means after the H-relay is switched and before the line is released.