A saddle device includes a first seat unit (10) having a front mounting portion (12) and a rear mounting end portion (42), a saddle unit (30) having a front end portion unit (314') and a top surface unit (32), and an elongate backrest (50) including two spaced-apart long sides (51, 52), and two spaced-apart short sides (53, 54) that are connected between the long sides (51, 52), and removably mounted to a selected one of the front mounting portion (12) and the rear mounting end portion (42) such that, when the backrest (50) is mounted to the front mounting portion (12), at least one of the short sides (53, 54) is located in front of the front end portion unit (314'), and when the backrest (50) is mounted to the rear mounting end portion (42), at least one of the long sides (51, 52) is located above the top surface unit(32).