A fitting connector includes: a first connector; a second connector; a detection member that is relatively movable to a main locking position with respect to a housing when the housings are completely fitted to each other and is locked to the housing at the main locking position; and first and second holding structures which keep the completely fitted state, in which the first holding structure includes a first locking holder for the housing with a locking portion and a second locking holder provided in the counterpart housing and entering the locking portion to regulate the relative movement between the housings in the completely fitted state, in which the second locking holder includes a protrusion portion entering the locking portion and a flexible portion capable of moving the protrusion portion in a direction opposite to the insertion direction toward the locking portion while being bent.