Abstract: An automatic loading amount control apparatus for a granular compound fertilizer material includes a grain size distribution measurement module, a control module, a control table, and a material loading amount control module. The grain size distribution measurement module and the control module periodically measure the weight-converted grain size distribution of a formed granular compound fertilizer and calculate a center grain size and a yield on the basis of the measured grain size distribution. The control table holds the maximum yield of the granular compound fertilizer and a center grain size providing the maximum yield. The control module updates the maximum yield and the center grain size held in the table on the basis of the center grain size and the yield calculated by the grain size distribution measurement module.