The invention relates to the technical field of automation of a substation of an electric power system, specifically to a secondary equipment apparatus. A power supply module of the secondary equipment apparatus is arranged in a power supply module shell; the power supply module shell is arranged on the exterior of a machine case, so that the power supply module can be independently arranged on the exterior of the machine case; therefore, influence to normal operation of other electrical modules in the machine case from heating of the power supply module can be avoided, electromagnetic interference of the electrical modules to the power supply module also can be avoided, and the stability of the secondary equipment is improved; the power supply module is arranged on the exterior of the machine case, so that when operation failure warning occurs to the power supply module, the power supply module can be replaced simply and rapidly, and power cut time caused by the power supply module failure can be greatly shortened; meanwhile, by virtue of the independent setting of the power supply module, operation to the power supply module in the later-period overhaul and maintenance also becomes convenient; and when the secondary equipment has a failure and needs to be replaced, the power supply module can be reserved, so that the maintenance cost and replacement cost are lowered.