The transducer-protector device for medical apparatus comprises a housing formed by two half-shells, a membrane defining a gas-permeable anti-contamination barrier, a female Luer first connection port, a second connection port for connection to a flexible tube, a helical bellows-conformed deformable member. The device, which operates in a service line of an extracorporeal blood circuit associated to a dialysis machine, is for protecting the machine from contaminating agents originating from the circuit. The device is simple and economical to manufacture.