A substrate includes a primary circuit; a secondary circuit; and a ground (GND) patterns. In a path between the primary circuit and the secondary circuit without passing through the GND pattern, reinforced insulation is provided between the primary circuit and the secondary circuit. In a path between the primary circuit and the secondary circuit through the GND pattern, one of 1) a combination of reinforced insulation and functional insulation and 2) a combination of basic insulation, additional insulation, and functional insulation is provided between the primary circuit and the secondary circuit.