PURPOSE: To reduce the stray capacity of a rotary transformer and to enhance its transmission characteristic.

CONSTITUTION: In a rotary transformer, a plurality of coil grooves 13b are formed in faces which are faced by keeping a gap and on which a stator core and a rotary core are faced and windings 15b are formed respectively inside the coil grooves 13b. (1) In the rotary transformer, guide members for the windings 15b are formed inside the coil grooves 13b and each interval between the windings is kept at a desired distance. Thereby, a stray capacity between the windings 15b can be reduced and a transmission characteristic can be enhanced. (2) In the rotary transformer, recessed and protruding parts 17 which guide the windings 15b are formed in the coil grooves 13b themselves. Thereby, each interval between the windings can be kept at a desired distance, the stray capacity between the windings 15b can be reduced and the transmission characteristic can be enhanced.