To provide a synthetic resin made tube fitting capable of avoiding concentration of stress to a branch part on the synthetic resin made tube fitting of cheese, elbow, etc., and an inside part of a bent part while restraining increase of product weight to the minimum.

A stepped part 21 of an inside part 17 of a branch part and a bent part of a stopper 16 for connecting pipe end part contact provided at a socket deep part of a fitting is formed higher than a stepped part 22 of an outside part 18 of the branch part and the bent part.