<；P>；PROBLEM TO BE SOLVED: To provide a speed changing device improved in operability by reducing an operation force when rolling up a greenhouse sheet, and also improved in an operation efficiency when unwinding by increasing an unwinding speed when unwinding the greenhouse sheet to shorten the necessary time, and to provide a greenhouse opening and closing device with the speed changing device. <；P>；SOLUTION: This speed changing device for selectively outputting constant speed transmission and variable speed transmission of input into an input shaft to an output shaft connected in series therewith is so formed that a second coupling of a transmission speed switching plate is coupled with a second shaft 22 by movement operation of a switching operating member 4 so as to directly link a first shaft 21 and the second shaft 22 and perform constant speed transmission, and a first coupling of the transmission speed switching means is coupled with a first gearwheel 23 by movement operation of the switching operating member so that the first gearwheel 23 performs variable speed transmission by coupling the first shaft 21 and the second shaft 22 with a transmission gearwheel as a transmission member. <；P>；COPYRIGHT: (C)2010,JPO&INPIT
