[PROBLEMS] A resin-made flat encapsulation container in which the problem of a reduction in mechanical strength caused by a reduction in the amount of resin is reasonably solved. [MEANS FOR SOLVING PROBLEMS] In the resin-made flat encapsulation container having side surfaces (50) with a smaller width than front and rear surfaces (30), the front and rear surfaces (30) are formed as curved surfaces protruding in either or both of the direction (S) of the main axis connecting a mouth section (13) and a bottom section (15) of the container and the direction (T) normal to the main axis direction (S). At least one pressure regulation surface (31a, 31b) is formed on the front and rear surfaces (30). The pressure regulation surface is curved such that it is protruded in either of the main axis direction (S) and the direction (T) normal to the main axis direction (S) and recessed in the other.
