The effect of avoided voidable act under section 176 is that such act shall be deemed void ab initio and the parties shall be restored to his previous position. As Thailand legal system uses single contract system, the effect of obligation and transfer of property are inseparable. In order to create conclusive standard regarding impossibility on restoration, the effect of obligation and transfer of property must be taken into consideration separately. In Thailand, the effect of avoidance act is to restore parties’ position to unbind relationship in obligatory aspect. As for transfer of property, he must return what he previously received from avoided act and for money; the restoration can be made in kind. The avoidance is unilateral juristic act aims to extinguish the validity of avoidable act so it cannot create legal obligation to the party who has no intention to be obliged from the beginning. Therefore, the restoration after avoidance is legal “duties”. In Germany, the avoidance only extinguishes obligatory effect. Consequently, the transferred property is deemed to lack of inquiring legal basis and such property shall be returned on grounds of unjust enrichment. On the other hand, due to single contract system in France, the avoided act does not affect the transfer of property so in order to restore parties to their previous position, the property shall be returned on restitution basis. For the general things, the restitution in kind can be made. If such is impossible, the parties shall make the restitution in value instead. However, the restitution does not limit the parties’ rights to claim for damages under Tort and Pre-contractual liability. The author proposed the adoption of separation contract system; as a result, the restoration of property will be based on unjust enrichment. However, adopting different contract system cannot be made with specific type of contract, so the author proposed the following guidelines. 1. Interpretation of Section 176 that the impossibility of restoration means impossibility in transfer of property. The generic things cannot perish and the partial impossibility can exist for the immovable property. In such case, the parties shall return what can be returned and indemnify the value for the possibility part. As the restoration is legal duties, the calculation of interest of money paid cannot be the same with Section 214 and when comprising with interpretation of Paragraph 2, relating to knowing the cause of voidable act, which aims to protect those who acts in good faith. Types of person that the law aims to protect must not be enforced to restore money or benefits exceeding of what he received. The interest rate shall be calculated from the date that the judgment has been rendered by court. As for restoration from lease, the restoration shall be indemnified with money value instead. 2. Amendment of the law of things by including section on fungible things
