Abstract: A watch main-body mounting seat 16, which is part of a watchband 14 of a watch 10 that can serve as either a wristwatch or a clock, has a circular hole 20 at the center. A notch-1 22 and a notch-2 24 are formed oppositely along the circumference of the seat hole 20. The back face of the watch main-body mounting seat 16 is provided with a guide groove-1 26 and a guide groove-2 28 extending counterclockwise from the notch-1 22 and the notch-2 24, respectively. An engaging projection 30 and an engaging projection 32 are formed to protrude on the back face of the watch main body 12. An engaging tab-1 30A and an engaging tab-2 32A extend laterally from the end of the engaging projections 30 and the engaging projections 32, respectively. The watch main body 12 is provided with bases 44 and 46 and a ring 48.