Crystal oscillating piece and crystal oscillator

A crystal oscillating piece according to the present invention is characterized by: being formed in a plate shape, said piece being provided with an AT-cut crystal piece formed in a rectangular shape when viewed from the direction of a normal to the principal surface thereof, and a first external electrode and a second external electrode that are provided to the principal surface so as to be aligned along the short-side direction along which the short side of the principal surface extends; the long side of the principal surface being substantially parallel to the Z' axis of the crystal piece, the short side of the principal surface being substantially parallel to the X axis of the crystal piece, the frequency of principal vibration of the crystal piece being 20.0-60.0 MHz, and 0.050≤P≤−0.0047×F+1.728, where the short-side-direction interval between the first external electrode and the second external electrode is represented by P (mm) and the frequency of principal vibration of the crystal piece is represented by F (MHz).