Provided is an endoscope that can connect proximal ends of the first signal lines and a signal relay part together without securing an extra length for the first signal lines. An airtight casing is disposed inside an outer tube of an insertion part, an imaging device and first signal lines are accommodated inside the airtight casing, a distal end of the airtight casing is airtightly sealed by a cover glass, and a proximal end of the airtight casing is airtightly sealed by a partition wall part. The airtight casing is constituted of a first tubular body and a second tubular body, and the second tubular body is disposed in a nested shape with respect to the first tubular body. During the connection between the proximal ends of the first signal lines and the terminal part, the second tubular body is advanced toward the first tubular body.