The ornamental design for a stepperexercisedevice, as shown and described.
FIG. 1 is a perspective view of a stepper exercise device showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a top view thereof.
A bottom view thereof is omitted since it does not contain ornamental features. The broken line portions of the stepper exercise device in FIGS. 1-7 represent unclaimed portions of the claimed design and form no part thereof.