To resolve the problem that the synthetic resin container used in a microwave oven, of which a fit part is formed between the container body and the lid body to be fitted thereto so that the fit part is firmly fitted while being cooled and is loosened as the container expands in accordance with an increased temperature to release air and steam generated inside the container, causes contamination due to, for example, soup stock splattering inside the microwave oven by boiling steam pressure burst-opening the lid body from the loosened gap.

Narrow flanges 23A and wide flanges 23B are continuously integrally formed in the outer circumference of a food accommodating portion shaped in a concave in the middle part of a container body 20. A lid body 30 has an outer shape the same with the container body 20. The lid body 30 formed with finger hook portions 34 shaped in upward convexes on wide flanges 33B, and ribs 35 on an inner side of flanges 33 other than the finger hook portions 34. The lid body 30 is fitted onto the container body, thereby, steam paths 40 communicating in a longitudinal direction are formed from the finger hook portions 34 and the faces of the flanges 23B, respectively.