An illumination lens is formed of one lens, and an aspherical surface is formed on an incident surface on which light generated from a light source is to be incident so that the incident surface has a convex shape in a paraxial region. In a case in which the amount of sag at each point on an aspherical surface corresponding to a height from an optical axis is expressed by a function of h, predetermined Conditional Expression, which is related to a height at which a second derivative of the function with respect to h is 0 and the maximum height of the aspherical surface, is satisfied. Predetermined Conditional Expression related to a refractive index of the illumination lens is satisfied.
