A power plant mounting apparatus includes a mount member that enables a side member of a vehicle to support a power plant. The mount member has a supporting member whose one end is fixed to the power plant. The supporting member has a shaft portion at the other end thereof which is disposed within an outer tube. An insulator is provided between the shaft portion and the outer tube. A bracket of a flat plate-shape attached to the outer tube is fastened to an inner side surface of the side member by means of a bolt. A center point of the shaft portion within the outer tube is positioned within the side member.