To provide a guide core capable of being detachably attached to an insert body and an insert body to which the guide core can be detachably attached, the present invention provides a guide core able to be attached in a detachable way to an insert body, comprising a supporting portion capable of supporting an external terminal face of an area array type electronic component so that external terminals of the area array type electronic component are exposed to the direction of connection terminals of a socket, and a hook receiver able to be engaged in a releasable way with a hook portion provided to the insert body, and an insert body able to be attached in a detachable way with the guide core, comprising an electronic component guide portion comprising a guide core attachment socket to which the guide core is attached, and an electronic component inlet connected with the guide core attachment socket so that an electronic component can be guided to the guide core attached to the guide core attachment socket, and a hook portion able to be engaged in a releasable way with a hook receiver provided to the guide core.