Abstract: A coupling device includes male and female couplings having first and second circumferential grooves on surfaces of the respective couplings that face each other when the couplings are fitted together. The coupling device further includes an engaging member. When the male coupling is pushed into the female coupling, the engaging member is retracted into the second groove, allowing the male coupling to be inserted into the female coupling, and when the couplings are fitted together, the engaging member is pushed into the first groove by coil springs so as to be fitted into both of the groove, thereby preventing separation of the male and female couplings in the axial direction. Countersunk head screws support respective divided pieces of the engaging member. Slotted head setscrews are screwed in at boundaries between the adjacent divided pieces to press the divided pieces against the bottom of the first groove.