A packing mounting structure, comprising: a casing configured to house a power detection terminal, and that includes a passage part on a wall part configured to face the power detection terminal, the passage part connecting an external space with an internal space of the casing; a packing that includes a seal part configured to close the passage part, and a portion to be held protruding toward an axis direction of the seal part from the seal part; a cover that includes a hole part, that is configured to be installed on the casing in a state in which the portion to be held is held by the hole part, and that closes the passage part by the packing; and a fastening member that is configured to fasten the casing and the cover to a device serving as an object to which the casing and the cover are to be mounted, characterized in that the portion to be held includes a shaft part, a first flange part disposed on a tip end part of the shaft part, and a second flange part disposed on a position closer to the seal part in the shaft part, and the hole part includes a narrow part having a narrower width than an outer diameter of the shaft part; an insertion hole part that is linked to one end of the narrow part, and that has a planar shape through which the first flange part is capable of passing; and a holding hole part that is linked to another end of the narrow part, that has a planar shape through which the first flange part is incapable of passing, and that is configured to hold the shaft part in a state in which a gap is formed between the holding hole part and the shaft part. a casing configured to house a power detection terminal, and that includes a passage part on a wall part configured to face the power detection terminal, the passage part connecting an external space with an internal space of the casing; a packing that includes a seal part configured to close the passage part, and a portion to be held protruding toward an axis direction of the seal part from the seal part; a cover that includes a hole part, that is configured to be installed on the casing in a state in which the portion to be held is held by the hole part, and that closes the passage part by the packing; and a fastening member that is configured to fasten the casing and the cover to a device serving as an object to which the casing and the cover are to be mounted, characterized in that the portion to be held includes a shaft part, a first flange part disposed on a tip end part of the shaft part, and a second flange part disposed on a position closer to the seal part in the shaft part, and the hole part includes a narrow part having a narrower width than an outer diameter of the shaft part; an insertion hole part that is linked to one end of the narrow part, and that has a planar shape through which the first flange part is capable of passing; and a holding hole part that is linked to another end of the narrow part, that has a planar shape through which the first flange part is incapable of passing, and that is configured to hold the shaft part in a state in which a gap is formed between the holding hole part and the shaft part. a narrow part having a narrower width than an outer diameter of the shaft part; an insertion hole part that is linked to one end of the narrow part, and that has a planar shape through which the first flange part is capable of passing; and a holding hole part that is linked to another end of the narrow part, that has a planar shape through which the first flange part is incapable of passing, and that is configured to hold the shaft part in a state in which a gap is formed between the holding hole part and the shaft part.