A base side connecting mechanism (30) comprises a holder (40), a plug metal (50) and a sleeve (70). The plug metal (50) has a shaft (51) and a lock pin (52) projecting from the shaft (51) in a radial direction. The sleeve (70) is disposed to move slidingly along an axial direction of the shaft (51), is supported by the plug metal (50) through a wave washer (60), and receives biasing power toward an antenna mast (100) side. A mast side connecting mechanism (120) comprises a circular cylinder portion (121). The circular cylinder portion (121) is formed to press the sleeve (70) along the axial direction and has loosely penetrated portions (124, 125) in which the lock pin (52) can move along a circumferential direction and in which other end portions are large-diameter.