An inflation viewing device has a main body which is externally provided with a transparent viewing portion and internally provided with an inner passage where an air path assembly is arranged. An air entrance connector is operatively connected to an external air source and to a first end of the main body. An air exit connector is connected to a second, opposed end of the main body and to an inflation valve. A guide spacer is provided between the air entrance connector and the main body. The guide spacer has an inner passage having a wider section in communication with the inner passage of the main body and a reduced section defining a communication opening with the air entrance connector. A filter is arranged in the communication opening. A plunger, biased by a spring, is slidably arranged within the inner passage of the guide spacer and guide section of the main body inner passage.