An infant carrier device comprises a foldable support frame, an adjustable backrest assembly, a backrest positioning mechanism including a fixed positioning member and a movable latching member connected with the backrest assembly, and a disengaging mechanism connected with the support frame and movable relative to the positioning member. The latching member is movable between a first position where the latching member is engaged with the positioning member for locking the backrest assembly in position, and a second position where the latching member is disengaged from the positioning member. Moreover, the disengaging mechanism is operable to interact with the latching member for causing the latching member to move from the first position to the second position when the support frame is folded.