To reduce the occupying area of a crystal oscillator and also to reduce the assembly time by making a heater with a substrate formed by being bent in a U shape and arranging a crystal plate located inside the case for the crystal oscillator at a surrounding position on a U-shaped inner side.

A heater 1 is located between a crystal plate 2 and a case 3, is shaped in a U shape so as not to come into contact with the plate 2 and the case 3 respectively and is electrically connected to the outside by a terminal 7. The heater 1 is subjected to heat generation by power applied to the terminal for the temperature control of the plate 2, and the plate 2 is heated by the rise of the atmosphere temperature caused by the temperature rise of filler gas due to heat generation and radiation from the surface of the heater 1. Since the temperature control of the plate 2 of a crystal oscillator can be performed without putting the heater around the outer part of the crystal oscillator, the occupying area of the crystal oscillator can be reduced, and heater mounting work can be reduced so that a crystal oscillator small-sized and inexpensive can be obtained.