A resonator element includes: a base portion; and a resonating arm extending in a first direction from the base portion, wherein the resonating arm includes a first surface, a second surface facing the first surface, a first side surface extending in the first direction so as to connect the first and second surfaces, and a second side surface facing the first side surface, wherein the resonating arm includes a first width portion having a first width and a second width portion provided at a root of the resonating arm so as to have a second width larger than the first width, wherein the resonating arm includes a groove portion provided on at least one of the first and second surfaces so as to extend in the first direction, the groove portion in the second width portion having a width larger than a width of the groove portion in the first width portion, and wherein a sum of the width between the groove portion in the second width portion and the first side surface and the width between the groove portion in the second width portion and the second side surface is smaller than a sum of the width between the groove portion in the first width portion and the first side surface and the width between the groove portion in the first width portion and the second side surface.