An electric circuit device and related manufacturing method are disclosed as having a case incorporating therein a substrate on which electric circuit elements are mounted. A sealant is filled in the case to cover the electric circuit elements and the substrate and is composed of a lower layer gel and an upper layer gel formed in a two-layer structure. The upper layer gel has a penetration equal to or less than 90 and the lower layer gel has a penetration greater than that of the upper layer gel to allow the upper layer gel to suppress vibration of a surface of the lower gel for thereby suppressing the deformation of the lower layer gel even in the presence of a tendency causing the electric circuit elements or the substrate to vibrate, preventing a degraded function in insulation, waterproof and vibrational relaxation of the lower layer gel.