In our everyday lives, we are exposed to many stressors that induce mental stress, and consequently people may suffer mental illness, such as depression, bipolar mood disorders, and so on. Although there are many empirical studies showing that smelling an aroma or eating/drinking something is useful for easing mental stress, those studies did not use standardized methods for evaluating stress and/ or for easing stress. Preceding studies also used simple and boring tasks, such as the Kraepelin test requiring mental subtraction of a number sequence. In this study, a convenient task using SUDOKU puzzles for evoking mental stresses was introduced. Then, effective methods for easing stresses were investigated. This study revealed that the aromas of coffee and orange had a suppressive effect on stress, but the aromas of grapefruit and hinoki did not suppress mental stress. Also drinking canned coffee, bottled water, cola drink, or eating chocolate did not have a suppressive effect on mental stress. This study suggests that using coffee or orange aroma as an ambient odor suppresses mental stress.