A tire inside information acquiring device (100) attached inside a tire-wheel assembly, includes a housing body (10) configured to house a receiving antenna for receiving a radio signal and an electronic circuit unit connected to the receiving antenna, the electronic circuit unit constitutes the tire inside information acquiring device (100), and a substrate (40) on which the housing body (10) and a component constituting the tire inside information acquiring device (100) are disposed. The housing body (10) is formed of a nonmetallic inorganic material. The component is only formed of parts having water resistance.