Tire information detecting apparatus having improved reception sensitivity

A tire information detecting apparatus includes an interrogator (40) provided to the main body of a vehicle and each of the responders (20) provided to each of the tires (11) of the vehicle and responding to the interrogator (40). Each of antenna units (30) having an antenna, a mixer, and a branching filter is provided in the vicinity of each of the tires and is connected to the interrogator via cables. The mixer includes an interactive mixer, which has a first port and a second port connected interactively with each other, and a third port. The first port of the mixer is connected to the antenna, the second port is connected to the high frequency side port of the branching filter, the third port is connected to the low frequency side port of the branching filter, and a common port of the branching filter is connected to the cables.