A device for mounting a spark plug in a combustion chamber of a gas turbine engine includes a chimney including a collar extending radially inwards, a washer fastened on an axial end of the chimney so as to project towards the inside of the chimney, and a bushing forming a spark plug guide and including an inner collar and an outer collar that are axially spaced apart from each other by a cylindrical portion. Each collar extends radially outwards. The bushing is floatingly mounted inside the chimney with its collars axially positioned between the collar of the chimney and the washer. The inner collar comes in operation to bear against the collar of the chimney. The outer collar presents an outside diameter (d1) greater than the inside diameter (d2) of the washer.