A power transmission device has a rigid body that includes a contact portion coming into contact with the first or second friction member and that moves the contact portion from a position of contact with the first or second friction member to a position of no contact with the first and second friction members, an elastic body that applies to the rigid body a force moving the contact portion to a position of contact with the first or second friction member, a first pushing mechanism that applies to the rigid body a pressure of liquid moving the contact portion to a position of contact with the first or second friction member, and a second pushing mechanism that applies to the rigid body a pressure of liquid moving the contact portion to a position of no contact with the first and second friction members.