Waterproof socket and illumination apparatus

A waterproof socket, comprising:

• a socket body having an insertion hole to which a lamp pin protruding from an end cap of a straight tube lamp is inserted, the straight tube lamp being mounted to the waterproof socket by rotating the straight tube lamp about a center axis thereof;
• a tightening cover for covering the end cap of the straight tube lamp mounted to the socket body, the tightening cover being tightened to the socket body by thread coupling about the center axis;
• a first internal sleeve making contact with the socket body;
• a tubular seal for restraining moisture from infiltrating through between the straight tube lamp and the tubular seal;
• and
• a second internal sleeve for accommodating the seal and pressing the seal against the first internal sleeve upon tightening the tightening cover,
• wherein the first internal sleeve, the seal and the second internal sleeve being arranged between the socket body and the tightening cover in the named order from the socket body toward the tightening cover and the straight tube lamp is inserted through the second internal sleeve, the seal, and the first internal sleeve,
• wherein the socket body includes a body-side rotation restraint portion engaging with a sleeve-side rotation restraint portion formed in the first internal sleeve to restrain the first internal sleeve from rotating about the center axis, and
• wherein the first internal sleeve includes a first position restraint portion and the second internal sleeve includes a second position restraint portion engaging with the first position restraint portion of the first internal sleeve to restrain the second internal sleeve from rotating about the center axis while allowing the second internal sleeve to move in an axial direction of the straight tube lamp.