Housing structure of electronic keyboard musical instrument

A housing structure of an electronic keyboard musical instrument having a housing comprised of lower and upper cases which are separate from each other, the upper case being adapted to be pivoted relative to the lower case between open and closed states and the housing being completed by fixing the upper case which is in the closed state to the lower case, comprising:

• at least one protrusion fixedly formed in either one of rear end portions of the upper and lower cases;
• and
• at least one engagement hole formed in another of the rear end portions of the upper and lower cases,
• wherein the upper and lower cases are adapted to be pivoted relative to each other in an opening and closing direction around an engagement portion between the engagement hole and the protrusion inserted into and engaged with the engagement hole, and
• wherein the protrusion and the engagement hole are adapted to be relatively inserted into and removed from each other in a direction in which the protrusion is projectedly formed only when the upper case is at a predetermined pivotal angle in a pivotal movement in the opening and closing direction.