To firmly support a drain pipe joint by improving the strength of a support mechanism for drain pipe joint.

The support mechanism 50 for drain pipe joint is a support mechanism for supporting a drain pipe joint comprising an upper body 21a including an upper socket 22, a lower body part 21b having a horizontal branch pipe socket 25 formed on a side surface and a pipe connection part 27 formed on a lower part, and flange parts 41 and 42 connecting the lower body part 21b to the upper body part 21 in a watertight state. The mechanism comprises a support bracket 52 having a fixing part 53 fixed to a surface of a concrete slab CS and a protruding part formed to protrude horizontally to the fixing part 53; and a flange support member 60 having a structure displaceable in the height direction, which is installed to the tip of the protruding part of the support bracket 52, and supports the flange parts 41 and 42 while being fitted to bolts in the flange parts 41 and 42 of the drain pipe joint 20 from below.