An environmental chamber includes a testing tub in which a testing space is formed. The testing tub has a front wall, a left sidewall, a right sidewall, a rear wall, and a ceiling part, and is divided into a lower tub part and an upper tub part by a dividing surface extended in a direction inclined downwardly and frontwardly. The left and right sidewalls are respectively divided into two portions by the dividing surface. An inner surface of the upper tub part includes at least a part of an inner surface of each of the ceiling part, the front wall, the left sidewall, and the right sidewall. The upper tub part is supported by the lower tub part to be able to open the testing space.