To provide a tube fitting for an inner auxiliary tube through which an inspector can visually confirm whether there is abnormality in a conduit in a manhole or not and a manhole structure using this tube fitting.

This tube fitting F for an inner auxiliary tube is constituted of a transparent four-way type fitting main body 1 having a socket 11 to which an end part of an inflow pipe 8 is connected on one end part in the horizontal direction, having a socket 13 to which an upper end spigot 91 of the inner auxiliary tube 8 is connected on a lower end part in the vertical direction and formed so that a tube axis of the socket 11 and a tube axis of the socket 13 orthogonally cross with each other.