A calculation on the temperature variation in magnetization for iron metal is performed based on the band model, by making use of the density of states curve which was determined from the experimental data for the low temperature specific heat. The effective exchange energy is expanded in a power series of magnetization and the values of coefficients are estimated by comparing the calculated and experimental results of the temperature variation in magnetization. In order to explain the experimental results for the temperature variation, the terms of higher powers of magnetization than the quadratic must be taken into account. Above the Curie temperature, the temperature variation in the molecular field coefficient is estimated from the comparison between the calculated and experimental results of the temperature dependence of the magnetic susceptibility.