A cannula device including: a nasal cannula having nasal pipes; respiration-gas flow tubes connected to the nasal cannula; an adaptor pipe communicated with the respiration-gas flow tubes; a connector pipe removably attached to the adaptor pipe; and a respiration-gas supplying tube connected to the connector pipe, in the cannula device, one of the adaptor pipe and the connector pipe is a female member having a receiving part and the other is a male member having an inserting part; and the male member is removably inserted into the female part, and the cannula device further including: a ring-shape part formed on a base-end part of the inserting part as a protruding ridge or a recessed groove extending on whole circumference of the inserting part; and a lock piece formed on the receiving part, having a projection part locking the ring-shape part of the inserting part inserted in the receiving part.