A power transmission device comprising: a first rotating body rotated by a first drive mechanism; a second rotating body rotated by a second drive mechanism; and a clutch mechanism switching (26; 110; 210) between an engaged state and a disengaged state of the first rotating body and the second rotating body, wherein the clutch mechanism (26; 110; 210) has an engagement portion (50; 212) that includes a first friction member connected to the first rotating body and a second friction member connected to the second rotating body and disposed to face the first friction member, and that engages the first rotating body with the second rotating body by contact of the first friction member and the second friction member, a rigid body (52; 120; 220) that includes a contact portion coming into contact with the first friction member or the second friction member, and that moves the contact portion from a position of contact with the first friction member or the second friction member to a position of no contact with the first friction member and the second friction member, an elastic body (54; 124; 224) that applies to the rigid body (52; 120; 220) a force moving the contact portion to a position of contact with the first friction member or the second friction member. a first pushing mechanism that applies to the rigid body (52; 120; 220) a pressure of liquid moving the contact portion to a position of contact with the first friction member or the second friction member, and a second pushing mechanism that applies to the rigid body (52; 120; 220) a pressure of liquid moving the contact portion to a position of no contact with the first friction member and the second friction member, said power transmission device being characterized by a torque converter connected to the second rotating body, wherein the first pushing mechanism uses circulating fluid of the torque converter as liquid or the second pushing mechanism (128; 38) uses circulating fluid of the torque converter as liquid. a first rotating body rotated by a first drive mechanism; a second rotating body rotated by a second drive mechanism; and a clutch mechanism switching (26; 110; 210) between an engaged state and a disengaged state of the first rotating body and the second rotating body, wherein the clutch mechanism (26; 110; 210) has an engagement portion (50; 212) that includes a first friction member connected to the first rotating body and a second friction member connected to the second rotating body and disposed to face the first friction member, and that engages the first rotating body with the second rotating body by contact of the first friction member and the second friction member, a rigid body (52; 120; 220) that includes a contact portion coming into contact with the first friction member or the second friction member, and that moves the contact portion from a position of contact with the first friction member or the second friction member to a position of no contact with the first friction member and the second friction member, an elastic body (54; 124; 224) that applies to the rigid body (52; 120; 220) a force moving the contact portion to a position of contact with the first friction member or the second friction member. a first pushing mechanism that applies to the rigid body (52; 120; 220) a pressure of liquid moving the contact portion to a position of contact with the first friction member or the second friction member, and a second pushing mechanism that applies to the rigid body (52; 120; 220) a pressure of liquid moving the contact portion to a position of no contact with the first friction member and the second friction member, said power transmission device being characterized by a torque converter connected to the second rotating body, wherein the first pushing mechanism uses circulating fluid of the torque converter as liquid or the second pushing mechanism (128; 38) uses circulating fluid of the torque converter as liquid.