An air flow rate measurement device disposed in an intake passage by passing through an insertion hole of an intake pipe of an engine to communicate inside and outside includes: a case having a bypass channel, a part of air flowing through the intake passage flows into the bypass channel; a flow rate sensor arranged inside of the case, and having a flow rate detector which detects a flow rate of air flowing through the bypass channel; and a humidity sensor arranged outside of the case, and having a humidity detector which detects a humidity of air flowing through the intake passage. A surface of the humidity detector is arranged to oppose a wall of the case through a clearance.