The invention provides an expansion valve which can realize a fixing structure with necessary durability and corrosion resistance by means of low cost during the process for fixing a power element with small diameter. During the process for inserting and fixing a guiding surface (12b) which is formed in the inner circumference of the opening of the cylinder (12) of the power element (100), 0 is formed at the gap between the guiding surface (12b) and the external diameter of the power element (100) so that the power element (100) can perform positioning without dislocation when the power element (100) is inserted into the cylinder (12); besides, a retreat surface (12c) is formed in the inner circumference of the cylinder (12), and is in parallel with the guiding surface (12b) from the guiding surface (12b) through the connecting surface (12d); and the connecting surface (12d) can contact the upper end of the external diameter of the power element (100) only by slowly toppling the cylinder to the inner circumference side during the process for riveting with the cylinder, so that no cracks occurred on the cylinder, and necessary durability and corrosion resistance can be realized.