An electronic apparatus comprising: a receiving member having an opening; an insertion member that is inserted through the opening and provided with a male thread on a peripheral surface thereof; and a fastening member that is provided with a female thread on an inner surface thereof threadably engaged with the male thread, adapted to fix the insertion member to the receiving member by engaging the female thread with the male thread, and adapted to cover the opening; characterized in that the electronic apparatus further comprises a first O-ring positioned between the insertion member and the fastening member and a second O-ring positioned between the fastening member and the receiving member, in a state in which the insertion member is fastened by the fastening member, wherein, when viewing each circular cross-section of the first and second O-rings (41, 42) along a surface parallel to a moving direction of the fastening member when fastening the insertion member by rotating the fastening member, a first point of each circular cross-section is pressed against a surface perpendicular to the moving direction, and a position displaced from a second point opposite to the first point of each circular cross-section is pressed against an inclined surface (12, 32) inclined to the moving direction, wherein the insertion member is provided with a first holding section that is recessed in a diametrical direction of the insertion member to hold the first O-ring, and wherein the fastening member is provided with a second holding section that is recessed in a diametrical direction of the fastening member to hold the second O-ring. a receiving member having an opening; an insertion member that is inserted through the opening and provided with a male thread on a peripheral surface thereof; and a fastening member that is provided with a female thread on an inner surface thereof threadably engaged with the male thread, adapted to fix the insertion member to the receiving member by engaging the female thread with the male thread, and adapted to cover the opening; characterized in that the electronic apparatus further comprises a first O-ring positioned between the insertion member and the fastening member and a second O-ring positioned between the fastening member and the receiving member, in a state in which the insertion member is fastened by the fastening member, wherein, when viewing each circular cross-section of the first and second O-rings (41, 42) along a surface parallel to a moving direction of the fastening member when fastening the insertion member by rotating the fastening member, a first point of each circular cross-section is pressed against a surface perpendicular to the moving direction, and a position displaced from a second point opposite to the first point of each circular cross-section is pressed against an inclined surface (12, 32) inclined to the moving direction, wherein the insertion member is provided with a first holding section that is recessed in a diametrical direction of the insertion member to hold the first O-ring, and wherein the fastening member is provided with a second holding section that is recessed in a diametrical direction of the fastening member to hold the second O-ring.