Neither. This is a graph of an increasing force.
Constant velocity is the same as uniform speed. It requires acceleration to remain zero (0). F=ma, so a constant force would result in a linear increase of acceleration. Acceleration is increasing non-linearly with time, so an increasing force must be applied.
It is meaningless unless you state the scale of both the axes.
However, if we assume that the graph has both linear scales, it depicts that acceleration
To explain a graph, the scale of both the axes need to be defined.