A quartz crystal resonator that includes an AT-cut quartz crystal blank including a first main surface and a second main surface that face each other and each of which has long sides extending in an X-axis direction of the quartz crystal blank and short sides extending in a Z′-axis direction of the quartz crystal blank, and a first side surface and a second side surface that are located adjacent to the long sides of the first main surface and the second main surface; a first excitation electrode and a second excitation electrode; and an extension electrode that extends from the first main surface to the second main surface along the first side surface and that is electrically connected to the first excitation electrode. Each the first and second side surfaces have a first m-plane face and a second m-plane face.