To provide an antenna mounting apparatus capable of corresponding to differences in the sizes of mounting holes by changing the design of a locking member.

A mounting screw 18 is inserted and fitted to a locking member 20 allowed to be inserted into a mounting hole 24 from a down direction and the tip part of the mounting screw 18 is from a down direction screwed into an antenna base 10. The locking member 20 projects four projections upward from a peripheral edge part, and in each projection, the lower part is integrally formed, the upper part is vertically divided into two parts, one of the divided upper parts is formed as a locking claw 20a, and the other part is bent to the inside like a V shape in its cross section and formed as an aperture arm part 20b. The upper end part of the aperture arm part 20b is abutted on the peripheral surface of a projected part of an antenna base 10 to form a groove 10d for regulating the upward and inward movement of the arm part 20b. The cross-sectional V shape of the aperture arm part 20b is deeper bent by clamping and screwing the mounting screw 18 and the tip of the locking claw 20a of which the lower part is integrally formed is expanded to the outside and turned to the peripheral edge part of the mounting hole 24. The length of the aperture arm part 20b is changed to change the expanding size of the locking claw 20a to the outside.