The invention provides an aluminum electrolytic capacitor and a sealing rubber thereof. On the premise that no overlarge load is applied to a capacitor element to deteriorate the characteristics of the capacitor element, the capacitor element is kept to be reliably isolated from the external air. Meanwhile, a lead terminal is inserted into the terminal insertion hole of the sealing rubber. The hole diameter of a wire insertion hole (52) is smaller than the external diameter of an external lead-out wire (22), the external lead-out wire (22) is forcibly inserted into the wire insertion hole (52) to be led out into an external aluminum electrolytic capacitor. Inside a terminal insertion hole (5), a conical guide surface (53) is formed between a round rod fitting hole (51) and the wire insertion hole (52), wherein the diameter of the conical guide surface (53) is gradually reduced. An insertion guiding part (222) is integrally arranged with the diameter of the end portion of the external lead-out wire (22) to be smaller than the hole diameter of the wire insertion hole (52), wherein the diameter of the insertion guiding part (222) is gradually reduced from a wire main body (221). The peripheral surface of the insertion guiding part (222) is provided with a conical inclined plane (223) formed at a specified angle.