Transmitter for tire state monitoring apparatus

A transmitter for a tire state monitoring apparatus that is easily connected to a wheel in an optimal manner. The transmitter includes a valve stem (11) connected to a wheel (5) to which the tire is attached. Electric components are mounted on a circuit board (12) to detect the state of the tire. A casing (10) accommodates the circuit board in the tire. The casing faces toward an outer circumferential surface (5c) of the wheel. A connecting portion (20) connects the casing to the valve stem pivotally about a line perpendicular to the axial direction of the valve stem. A pressing mechanism (35) presses the casing toward the outer circumferential surface of the wheel to restrict pivoting of the casing.