PURPOSE: To eliminate an unnecessary force to be acted on a printed substrate and to obtain a waterproofing device for the substrate which does not need excessive working step of releasing it from a die by composing to form a long recess in a direction perpendicular to the longitudinal direction of a case on a waterproofing filler.

CONSTITUTION: In a printed substrate device, a printed substrate 2 on which various electronic components 1 are mounted is disposed in a case 3 in which one side is opened. A waterproofing filler 4 is so poured in the case 3 in height as to cover the conductive section of the component 1, and cured. Symbol 4a denotes a long recess formed on the filler 4, its depth is so formed that the recess is formed in depth to arrive at the bottom of the case 3, and the recess has a length to arrive at both side faces of the case 3 in a direction perpendicular to the longitudinal direction of the case 3. Even if the case 3 is shrinked, the recess 4a formed on the filler 4 absorbs the shrinkage. Accordingly, the 'warpage' of the printed substrate device and the crack of the case 1 can be prevented.