A casing assembly for electronic equipment comprising a printed circuit board on which an exothermic electronic component is mounted, a casing for covering the printed board, and a base for attaching the casing to a wall body or a rail. The base is of a high heat conductive material and has a planar structure which results in a large contact area between it and the wall body or rail. A high heat conductive plate like cushioning member made of an electrically insulative material is interposed between the board and the base in contact therewith. The heat generated in the electronic component is released through the printed board and lead wires and through the cushioning member and the base to the wall body or rail. Preferably, where the casing is attached to the rail, a guide latch member and a pressure latch member are attached to the base. Where an auxiliary printed board is provided in addition to the printed board, the base, the printed board, the auxiliary frame and the auxiliary printed board are stacked in that order and covered with the casing. Where a programmer is attached to the casing, provision is made for attaching in either the horizontal or vertical direction. Where the functions of a basic module is insufficient, extended modules may be connected.