Opening/closing structure of opening/closing cover

An opening/closing structure of a cover, comprising:

• a casing having an opening;
• and
• a cover configured to be rotatable with respect to the casing to open/close the opening,
• wherein one of the casing and the cover is provided with a shaft part having a shaft, and the other of the casing and the cover is provided with a receiving part having an insertion opening in which the shaft is inserted,
• wherein one of the shaft part and the receiving part is provided with a protrusion on a part of an end surface in an axial direction, and the other of the shaft part and the receiving part is provided with a contact portion on a part of a facing surface which faces the end surface,
• wherein the protrusion circumvents contacting the contact portion when the cover is in a closed state in which the cover closes the opening,
• wherein, when the cover is in an open state in which the cover is opened, from the closed state, by a particular angle, the protrusion contacts the contact portion so as to be applied with a resistant force against rotation of the cover, and
• wherein the protrusion protrudes in the axial direction and extends along a rotation direction of the cover.