A seal structure or a sealing method that seals the housing (case) and allows the signal line to pass through a seal portion of the housing is provided. A recessed level difference is formed on at least one of junction faces of first and second housing units (case units) joined together, and, at a portion including the recessed level difference, a first sealing material (double-faced adhesive sheet), the signal line (flexible cable) or circuit unit, and a second sealing material are held between the first housing unit and the second housing unit. The adhesiveness and flexibility of the first sealing material and the elasticity of the second sealing material allow the signal line or circuit unit to pass through the seal portion while maintaining airtightness.