A main unit capable of allowing a sub unit to be detachably mounted to the main unit, the main unit being capable of being in communicative connection with the sub unit after the sub unit is detached from the main unit, the main unit comprising: a main body comprising a front shell and a rear shell that are opposite to each other, the main body having a groove located in the front shell, wherein a through hole is defined in a bottom of the groove, a main board is provided in the main body, and a first connector is provided on a side of the main board facing away from the groove; a main unit keyboard mounted in the groove and comprising a key part and a flexible circuit board that are connected to each other, wherein an end of the flexible circuit board facing away from the key part is provided with a second connector configured to match the first connector, the key part is received in the groove, the flexible circuit board passes through the through hole and extends into an inside of the main body, and the second connector is fastened to the first connector; characterised in that it further comprises: a support, wherein a receiving groove is defined in the front shell and matches the support, and the support is rotatable with respect to the main unit to be located at a first position or a second position, wherein at the first position, the support is located within the receiving groove; and at the second position, at least a part of the support is located outside the receiving groove, and the main board is configured to activate the main unit keyboard; and a camera assembly comprising a first camera and a second camera, wherein a thickness of the first camera is smaller than a thickness of the second camera, and when the support is located at the first position, at least a part of the support and the first camera are stacked. a main body comprising a front shell and a rear shell that are opposite to each other, the main body having a groove located in the front shell, wherein a through hole is defined in a bottom of the groove, a main board is provided in the main body, and a first connector is provided on a side of the main board facing away from the groove; a main unit keyboard mounted in the groove and comprising a key part and a flexible circuit board that are connected to each other, wherein an end of the flexible circuit board facing away from the key part is provided with a second connector configured to match the first connector, the key part is received in the groove, the flexible circuit board passes through the through hole and extends into an inside of the main body, and the second connector is fastened to the first connector; characterised in that it further comprises: a support, wherein a receiving groove is defined in the front shell and matches the support, and the support is rotatable with respect to the main unit to be located at a first position or a second position, wherein at the first position, the support is located within the receiving groove; and at the second position, at least a part of the support is located outside the receiving groove, and the main board is configured to activate the main unit keyboard; and a camera assembly comprising a first camera and a second camera, wherein a thickness of the first camera is smaller than a thickness of the second camera, and when the support is located at the first position, at least a part of the support and the first camera are stacked. a support, wherein a receiving groove is defined in the front shell and matches the support, and the support is rotatable with respect to the main unit to be located at a first position or a second position, wherein at the first position, the support is located within the receiving groove; and at the second position, at least a part of the support is located outside the receiving groove, and the main board is configured to activate the main unit keyboard; and a camera assembly comprising a first camera and a second camera, wherein a thickness of the first camera is smaller than a thickness of the second camera, and when the support is located at the first position, at least a part of the support and the first camera are stacked.