Tremendous amount of studies have done to examine the human mechanisms to compare magnitudes of different aspects using number comparison task, during which subjects were required to choose larger number as quick as possible among two one-digit numbers presented on left and right visual field for each. The results reached a consensus that it takes longer to respond if the difference between two numbers was relatively small (distance effect) and the parietal cortex plays the central role to compare numerical magnitudes. It is also known that the spinal reflex can be inhibited by the cerebral activity. Here we examined whether the amplitude of H-reflex, the EMG of gastrocnemius induced by the stimulation of GIa neuron in tibial nerve, the pathway of stretch reflex, is influenced by the activation of parietal cortex during number comparison task. During the experiment, subjects were lied in prone position with cross-shaped button in their dominant hand to choose left or right of a pair of digit appeared on a computer monitor located 60 cm ahead of their face. The stimuli were delivered 240msec after the presentation of a pair of digit and subjects were told to choose the appropriate digit as soon as possible. As a result, there was a significant interaction between the difference between the digits (large or small) and the side of digit to choose (left or right), that is, the amplitude of H-reflex became smaller if the difference between digits was large (small) and subjects had to choose left (right) digit. The result might be due to an activation of parietal cortex because of choosing digit against so-called SNARC effect.