In a quartz crystal unit, the unit comprising a quartz crystal resonator having a base portion, and first and second vibrational arms connected to the base portion, at least one groove being formed in at least one of opposite main surfaces of each of the first and second vibrational arms, a length of the base portion being less than 0.5 mm and an overall length of the quartz crystal resonator being less than 2.1 mm, at least one mounting arm protruding from the base portion and being formed between the first and second vibrational arms, the at least one mounting arm extending in a common direction with the first and second vibrational arms.