This invention provides a serotonin 5-HT3 receptor partial activator which has a serotonin 5-HT3 receptor activating action, in addition to its serotonin 5-HT3 receptor antagonism, and does not cause constipation as a side effect. Particularly, based on the finding that newly synthesized benzoxazole derivatives typified by the compounds of the following formula (2) have strong serotonin 5-HT3 receptor antagonism and serotonin 5-HT3 receptor activating action, this invention provides these benzoxazole derivatives as serotonin 5-HT3 receptor partial activators. In the above formula, R1 to R4 may be the same or different from one another and each represents a hydrogen atom, a halogen atom, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted lower alkenyl group or a substituted or unsubstituted amino group, or two groups of R1 and R2 may be linked together to form a ring structure, namely benzene ring; R5 represents a hydrogen atom, a substituted or unsubstituted lower alkyl group or a substituted or unsubstituted lower alkenyl group; and m is an integer of 1 to 4.