To provide a ceiling installing structure of a unit room without using a screw and a bolt for connecting a wall panel and a ceiling panel.

In this ceiling installing structure, the ceiling panel 2 and the wall panel 3 are installed by using a connecting tool 1. The connecting tool 1 is formed by vertically projecting a main projecting piece 1b and an auxiliary projecting piece 1c for forming a downward projecting hook claw 1d on the tip in the same direction by separating a void 1e, on a surface on the bending piece projecting directional side of a belt-like connecting tool body for forming a doglegged shape bending piece 1a on the upper end; and is formed into a structure for fitting an end part of the ceiling panel 2 in a recessed place 1h formed of the main projecting piece 1b and the doglegged shape bending piece 1a, by inserting a projecting piece 3c arranged on the upper end of the wall panel 3 into the void 1e formed between the main projecting piece 1b and the auxiliary projecting piece 1c.