This electrical connection socket for relaying exchange of electrical signals between a first electrical component and a second electrical component, is provided with: a signal pin which is inserted in a communication hole of a metallic casing so as to form a coaxial line path between the inner wall surface of the communication hole and the outer circumferential surface of the signal pin so that one end of the signal pin is electrically connected to a terminal of the first electrical component while the other end is electrically connected to a terminal of the second electrical component; and a holding member which holds the signal pin in the communication hole such that the outer circumferential surface of the signal pin is separated from the inner wall surface of the communication hole, wherein the characteristic impedance of a signal path formed by the signal pin in a first region where the signal pin is held by the holding member is smaller than a predetermined characteristic impedance which is a reference, and the characteristic impedance in a second region adjacent to the first region is larger than the predetermined characteristic impedance.