Connector drop-off prevention structure and connector drop-off prevention method

A connector drop-off prevention structure in which, after a pipe member (11) having in sequence from the tip a first flange (11a) and a second flange (11b) projectingly provided on the outer periphery in the vicinity of the tip, and a pipe-shaped connector (13) having a large diameter portion (13a) at one end and a small diameter portion (13c) at the other end connected via a step (13b) are joined by inserting the first flange (11a) into the inner periphery of the large diameter portion (13a), a drop-off prevention holder (14) is installed so as to straddle both the pipe member (11) and the connector (13),

• wherein the drop-off prevention holder (14) is a box-shaped member with one open face (14a);
• among a first face (14b) and a second face (14c) of the drop-off prevention holder (14), which are mutually opposing, a first cutout (14d) is formed in the first face (14b) so as to communicate with the open face (14a), the first cutout (14d) fitting onto the small diameter portion (13c) so as to abut against the step (13b), a throat portion (b) having a slightly smaller width than the outer diameter of the small diameter portion (13c) being formed partway along the first cutout (14d), a second cutout (14f) is formed in the second face (14c) so as to communicate with the open face (14a), the second cutout (14f) fitting onto the pipe member (11) so as to abut against the second flange (11b), and
• a swing fulcrum portion (14h) is projectingly provided on the second face (14c), the swing fulcrum portion (14h) being capable of engaging with the pipe member (11).