A 1,6-.beta.-glucan synthetase inhibitor is provided, having potent growth inhibition and having excellent safety. A compound is provided, capable of expressing in a wide spectral range and specifically or selectively, an antifungal effect based on its functional mechanism of 1,6-.beta.-glucan synthesis inhibition. Also provided is a drug, a salt or hydrate thereof, especially an antifungal that contains the compound. Concretely, provided is a compound of the following formula (I), its salt or hydrate, and a drug or antifungal containing, as the active ingredient, the compound, its salt or hydrate: ##STR00001##