Extract of pine nodules and its component, SJ-2, have been reported to have an inhibitory effect on catecholamine secretion induced by acetylcholine (a physiological secretagogue) in cultured bovine adrenal medullary cells. The present study aimed to determine the effect of pine nodule extract, Sho-ko-sen, on the autonomic nervous activity induced by mental stress (Uchida-Kraepelin arithmetic test) in healthy young students. Autonomic nervous balance was measured by power spectral analysis of heart rate variability using a standard hexagonal radar chart. Four 15-min repetitions of an arithmetic task served as an acute mental stressor that caused increases in two sympathetic parameters and an increase in one parasympathetic parameter in the placebo group, while no increases in sympathetic parameters but various changes in parasympathetic parameters were observed in Sho-ko-sen group. The present study demonstrated that acute arithmetic stress-induced increases in sympathetic and parasympathetic nervous activity were detected by the autonomic nervous balance assay in the placebo group, but that such increases in sympathetic nervous activity, at least, were cancelled in healthy young students who ingested Sho-ko-sen (pine nodule extract).