An extreme pressure agent and a friction coefficient modifier which comprises a compound having, in a molecule, a group represented by general formula (I): ##STR1## wherein R.sup.1, R.sup.2, and R.sup.3 each represents hydrogen atom or methyl group, and at least one of R.sup.2 and R.sup.3 represents hydrogen atom; a fluid resistant to seizure under load and a wear resistant fluid which each comprises the above additive or the above modifier; and a flame resistant fluid which comprises a thermally polymerizable substance, preferably the above compound. The extreme pressure agent and the friction coefficient modifier have excellent properties and are advantageously used for lubricating oil, metal working oil, and hydraulic oil. The flame resistant fluid suppresses vaporization of flammable substances by thermal polymerization to prevent fire when the fluid is exposed to a high temperature and is advantageously used as lubricating oil, metal working oil, hydraulic oil, heat treatment oil, and grease.