An electrical component holder contains an electrical component to be connected to an internal circuit of a vehicle-installed electrical junction box. The holder has a casing main body and a lid to be mounted on an upper surface of the casing main body. The casing main body has a box-like configuration that is open at a lower end so that the casing main body can be placed on an electrical component mounting section of the electrical junction box. The casing main body has an upper wall that defines a through-hole that receives and holds a support portion of a terminal member of the electrical component. The support portion of the terminal member is inserted into and secured to the through-hole so that the terminal member projects into a hollow interior of the casing main body. The terminal member is inserted into and secured to a terminal aperture in the electrical component mounting section, under the condition that the casing main body is attached to the electrical component mounting section.