Abstract: A tire pressure detector includes a casing that receives a battery unit and a signal generating unit therein and that is provided with an adaptor to engage an inflating valve of a tire. A switch unit is mounted in the adaptor for connecting electrically the battery unit and the signal generating unit, and includes a resilient disc member with a peripheral portion secured to an inner wall of the adaptor, and a central portion moving in accordance with pressure inside the tire. An annular conductive piece is disposed on an inward protrusion of the adaptor and is connected to the signal generating unit. A conductive tubular body is disposed on the central portion of the disc member and extends slidably through the inward protrusion of the adaptor. The tubular body has a peripheral flange projecting outwardly from an upper end thereof and extending above the conductive piece. A hollow conductive seat member is mounted in the adaptor above the tubular body. The seat member is connected to the battery unit.