A humidifier device to prevent warping, cracking and shrinking of elements in stringed or other musical instruments subject to modification by reason of a lack of moisture in the instrument carrying case. The device comprises a small, sealed housing detachably securable to the interior of the instrument case and provides a refillable and leak-proof reservoir which feeds water or other evaporatable fluid to the top, bottom and inner peripheral side walls of an absorbent ring when the reservoir is filled to capacity; and when partially full and in any position of the carrying case water feed to the absorbent ring is maintained along at least one of the absorbent ring walls. A control ring is further provided which is rotatable about the housing to increase or decrease the evaporation rate of water from the housing ports communicating with the absorbent ring.