To provide a synchronizer of a transmission for improving mass productivity, by reducing the number of part items.

This synchronizer of the transmission has a gear stage having a coupling sleeve, an insert key, a clutch gear, a balk ring and a sybchrohub, and a support synchronous force generating mechanism for converting force in the peripheral direction by relative rotation into support synchronous force in the axial direction for pressing the balk ring to the clutch gear, when the relative rotation is generated between the synchrohub and the balk ring, by generating frictional torque between a balk ring tapered cone surface and a clutch gear tapered cone surface in shifting, and is provided with a spring for energizing the insert key in the outer diameter direction, and energizing the balk ring to the initial position side in the axial direction.