A micro electrical mechanical system device includes a frame portion having an upper surface with a rectangular shape; a functional element; a beam portion extending from one of sides of the frame portion toward an opposite one and having a first side surface, a second side surface opposite to the first side surface, and upper and lower surfaces between the first and second side surfaces; and a movable portion supported on the beam portion inside the frame portion to be movable. The beam portion includes a constricted portion formed in the first side surface and the second side surface along the functional element, and having a main surface and two side surfaces facing each other. The movable portion includes a center portion having four corner portions and protruding portions extending from the corner portions and away from the frame portion and the beam portion.