An option contract for a purchase and sale made by one party becomes effective when the other party manifests the intention to complete the purchase and sale.
売買の一方の予約は、相手方が売買を完結する意思を表示した時から、売買の効力を生ずる。
If no period is provided in relation to the manifestation of intention referred to in the preceding paragraph, the party to the option contact may issue a notice of demand to the other party, specifying a reasonable period of time, to the effect that the other party is to give a definite answer as to whether or not that party will complete the sale within that period. In these cases, if the other party fails to give a definite answer within that period, the option contract for a purchase and sale by one party ceases to be effective.
前項の意思表示について期間を定めなかったときは、予約者は、相手方に対し、相当の期間を定めて、その期間内に売買を完結するかどうかを確答すべき旨の催告をすることができる。この場合において、相手方がその期間内に確答をしないときは、売買の一方の予約は、その効力を失う。