In a building box type plug-in modular rack structure for electronic equipment, a box-like shelf accommodates a plurality of printed circuit boards therein. A pair of side frames symmetrical in a right-and-left direction each has a recess at the upper end and a projection at the lower end for respectively mating with the projection and the recess of adjoining side frames. A framework is constituted by the pair of side frames and the shelf interposed between them. Covers cover the outer periphery of the framework. A plurality of frameworks are stacked and connected together by the recesses and the projections of the side frames. A top cover and a bottom cover respectively are fitted on the top and the bottom of the stack of frameworks.