When combined with a compound having an acetylcholine esterase inhibitory effect, an alkyl ether derivative represented by the following general formula [1] or its salt: [1] wherein R , R , R , R , m and n are each as defined in the description; synergistically enhances an anti-hypoxia effect. Thus, this combination is useful as a method of improving brain function. A medicinal composition containing the combination of the compounds as described above is useful in treating and preventing dysmnesia caused by intracerebral acetylcholine nerve hypofunction or selective cell death occurring in cerebrovascular dementia, senile dementia, Alzheimer's disease, after effect of ischemic encephalopathy and cerebral stroke.