Provided is an exercise device for a lower body capable of simultaneously performing anaerobic exercise for leg muscle strengthening and stretching and aerobic exercise such as cycle pedal exercise. The exercise device for a lower body includes a pair of base bars 11 parallelly aligned with each other and having an arc shape; connecting shafts 12 fixed to side surfaces of center parts of the base bars 11 to opposite each other and having a pivot coupling structure installed therebetween; a pair of rotary arms 14 laterally pivotally hinged to upper surfaces of the center parts of the base bars 11 and having heel support frames 13 such that both feet are seated on upper surfaces of the rotary arms 11 to simultaneously perform anaerobic (static) exercise and aerobic (dynamic) exercise for leg muscles; and spring members 15 resiliently supported between the rotary arms 11 and the connecting shafts 12 to inwardly bias the rotary arms 14.