在证券市场融资购买证券时，投资者所需缴纳的自备款。

It is the amount paid by the customer when using a broker's credit to buy or sell a security. Under Federal Reserve regulations, the initial margin required since 1934 has ranged from 40% of the purchase price up to 100%. Since 1974 the current rate of 50% has been in effect. Put writers are adversely affected by falling prices, call writers by rising prices. Consequently, the Options Clearing House calculates daily market movement in each option series. Favourable movements are credited to an option writer's account. Unfavourable movement results in a margin call by OCH and requires the prompt lodgement of sufficient collateral to cover the potential loss.