A pressure indicator comprising: a transparent tube having a first segment and a second segment, the first segment defining therein a first bore, the second segment defining therein a second bore, the first bore of the first segment having a diameter greater than the second bore of the second segment, the first segment being integrally formed with the second segment such that a tapered annular surface is formed between an inner surface of the first segment, which defines the first bore, and an inner surface of the second segment, which defines the second bore, wherein the first segment has an open end opposite to the second segment, the second segment has an end wall provided with a connection fitting defining therethrough an air channel, and the second segment is provided with a pressure-indicating scale at its outer surface; a slider mounted in the transparent tube, the slider being shaped as a generally hollow cylindrical body which has an open end and a closed end opposite to the open end thereof and defines therein an inner space, the slider has a central tube which extends from an inner surface of its closed end, through the inner space thereof, to go beyond the open end thereof; a coiled compression spring received in the inner space of the slider and fitted around the central tube of the slider, wherein one end of the coiled compression spring is urged against the inner surface of the closed end of the slider; and a cap having a central tube which defines therein a central hole and extends from an inner surface of the cap, the cap being threadedly mounted to the open end of the first segment of the transparent tube, an opposite end of the coiled compression spring being urged against the inner surface of the cap; whereby, when an external pressure source is connected to the connection fitting of the transparent tube, the slider can be pushed by a medium supplied from the external pressure source to move along the second bore and the first bore of the transparent tube so that the pressure of the medium can be measured; when the pressure of the medium exceeds a predetermined pressure, the slider is capable of being pushed to reach the tapered annular surface to allow excessive medium to be released into ambient environment via an annular gap between the slider and the tapered annular surface of the transparent tube. a transparent tube having a first segment and a second segment, the first segment defining therein a first bore, the second segment defining therein a second bore, the first bore of the first segment having a diameter greater than the second bore of the second segment, the first segment being integrally formed with the second segment such that a tapered annular surface is formed between an inner surface of the first segment, which defines the first bore, and an inner surface of the second segment, which defines the second bore, wherein the first segment has an open end opposite to the second segment, the second segment has an end wall provided with a connection fitting defining therethrough an air channel, and the second segment is provided with a pressure-indicating scale at its outer surface; a slider mounted in the transparent tube, the slider being shaped as a generally hollow cylindrical body which has an open end and a closed end opposite to the open end thereof and defines therein an inner space, the slider has a central tube which extends from an inner surface of its closed end, through the inner space thereof, to go beyond the open end thereof; a coiled compression spring received in the inner space of the slider and fitted around the central tube of the slider, wherein one end of the coiled compression spring is urged against the inner surface of the closed end of the slider; and a cap having a central tube which defines therein a central hole and extends from an inner surface of the cap, the cap being threadedly mounted to the open end of the first segment of the transparent tube, an opposite end of the coiled compression spring being urged against the inner surface of the cap; whereby, when an external pressure source is connected to the connection fitting of the transparent tube, the slider can be pushed by a medium supplied from the external pressure source to move along the second bore and the first bore of the transparent tube so that the pressure of the medium can be measured; when the pressure of the medium exceeds a predetermined pressure, the slider is capable of being pushed to reach the tapered annular surface to allow excessive medium to be released into ambient environment via an annular gap between the slider and the tapered annular surface of the transparent tube.