A power transfer device for a vehicle , the power transfer device comprising: a friction clutch configured to adjust a transmission torque to be transmitted from an input rotary member to an output rotary member ; a motor ; a worm speed-reduction gear mechanism including a worm that is provided on a shaft of the motor and a worm wheel that meshes with the worm ; a conversion mechanism configured to generate a pressing force in the friction clutch by converting a rotary motion of the worm wheel into a linear motion; and an electronic control unit configured to control a rotation angle of the motor , the electronic control unit being configured to repeatedly execute rapid increase control and gradual reduction control when the friction clutch is to be maintained in a fully engaged state such that the input rotary member and the output rotary member rotate integrally, the rapid increase control being a control mode in which the rotation angle of the motor is increased to a first rotation angle at a first speed gradient, the first rotation angle being larger than a required rotation angle that is required to maintain the friction clutch in the fully engaged state, the gradual reduction control being a control mode in which the rotation angle of the motor having been increased by the rapid increase control is reduced to a second rotation angle at a second speed gradient, the second rotation angle being larger than or equal to the required rotation angle and smaller than the first rotation angle, the second speed gradient being smaller than the first speed gradient. a friction clutch configured to adjust a transmission torque to be transmitted from an input rotary member to an output rotary member ; a motor ; a worm speed-reduction gear mechanism including a worm that is provided on a shaft of the motor and a worm wheel that meshes with the worm ; a conversion mechanism configured to generate a pressing force in the friction clutch by converting a rotary motion of the worm wheel into a linear motion; and an electronic control unit configured to control a rotation angle of the motor , the electronic control unit being configured to repeatedly execute rapid increase control and gradual reduction control when the friction clutch is to be maintained in a fully engaged state such that the input rotary member and the output rotary member rotate integrally, the rapid increase control being a control mode in which the rotation angle of the motor is increased to a first rotation angle at a first speed gradient, the first rotation angle being larger than a required rotation angle that is required to maintain the friction clutch in the fully engaged state, the gradual reduction control being a control mode in which the rotation angle of the motor having been increased by the rapid increase control is reduced to a second rotation angle at a second speed gradient, the second rotation angle being larger than or equal to the required rotation angle and smaller than the first rotation angle, the second speed gradient being smaller than the first speed gradient. the rapid increase control being a control mode in which the rotation angle of the motor is increased to a first rotation angle at a first speed gradient, the first rotation angle being larger than a required rotation angle that is required to maintain the friction clutch in the fully engaged state, the gradual reduction control being a control mode in which the rotation angle of the motor having been increased by the rapid increase control is reduced to a second rotation angle at a second speed gradient, the second rotation angle being larger than or equal to the required rotation angle and smaller than the first rotation angle, the second speed gradient being smaller than the first speed gradient. <EOS>