A coil spring configured to be disposed in a fluid passage to urge a valve element disposed in the fluid passage displaceably in a direction of a longitudinal axis of the fluid passage from an open position for opening the fluid passage toward a closed position for closing the fluid passage, the coil spring comprising: a valve support portion configured to support the valve element; a secured portion configured to be secured to an inner peripheral surface of the fluid passage; an expanding-contracting portion extending from the secured portion toward the valve support portion, the expanding-contracting portion being wound a plurality of turns so as to expand and contract in the direction of the longitudinal axis when the valve element is displaced between the closed position and the open position; and a connecting portion extending between the valve support portion and an end winding portion of the expanding-contracting portion that is located at an end of the expanding-contracting portion closer to the valve support portion; wherein the valve support portion has a support winding portion that is concentric with the expanding-contracting portion as seen in the direction of the longitudinal axis and is smaller in diameter than the expanding-contracting portion; and wherein the connecting portion has, as seen in the direction of the longitudinal axis: a first portion extending curvedly from the end winding portion so as to pass radially outward of the end winding portion while at least partially overlapping the end winding portion; a second portion extending contiguously from the first portion radially inward and passing through the valve support portion; a third portion extending contiguously from the second portion curvedly so as to overlap at least one of the end winding portion and the first portion; and a fourth portion extending contiguously from the third portion radially inward to the support winding portion of the valve support portion. a valve support portion configured to support the valve element; a secured portion configured to be secured to an inner peripheral surface of the fluid passage; an expanding-contracting portion extending from the secured portion toward the valve support portion, the expanding-contracting portion being wound a plurality of turns so as to expand and contract in the direction of the longitudinal axis when the valve element is displaced between the closed position and the open position; and a connecting portion extending between the valve support portion and an end winding portion of the expanding-contracting portion that is located at an end of the expanding-contracting portion closer to the valve support portion; wherein the valve support portion has a support winding portion that is concentric with the expanding-contracting portion as seen in the direction of the longitudinal axis and is smaller in diameter than the expanding-contracting portion; and wherein the connecting portion has, as seen in the direction of the longitudinal axis: a first portion extending curvedly from the end winding portion so as to pass radially outward of the end winding portion while at least partially overlapping the end winding portion; a second portion extending contiguously from the first portion radially inward and passing through the valve support portion; a third portion extending contiguously from the second portion curvedly so as to overlap at least one of the end winding portion and the first portion; and a fourth portion extending contiguously from the third portion radially inward to the support winding portion of the valve support portion. a first portion extending curvedly from the end winding portion so as to pass radially outward of the end winding portion while at least partially overlapping the end winding portion; a second portion extending contiguously from the first portion radially inward and passing through the valve support portion; a third portion extending contiguously from the second portion curvedly so as to overlap at least one of the end winding portion and the first portion; and a fourth portion extending contiguously from the third portion radially inward to the support winding portion of the valve support portion.