A tube connector that allows for a secure connection between a plug and a socket is provided. An accommodation space is provided such that, when the plug is inserted into an insertion hole of the socket while a sleeve is lifted upward to a base-end position, if a ball rolls on an outer periphery of the plug so as to come into abutment with a projection, the accommodation space entirely accommodates the ball at a side adjacent to the socket relative to the outer periphery of the plug.