A crystal oscillator with improved tolerance to radiation such as X-rays includes: a container body; a quartz crystal blank accommodated in a first recess formed on one main surface of the container body and hermetically encapsulated in the first recess by a metal cover; and an IC chip that integrates electronic circuits including at least an oscillator circuit using the crystal blank and is accommodated in the second recess formed on the other main surface of the container body. The IC chip is fixed to the bottom surface of the second recess by flip-chip bonding such that a circuit formation plane of the IC chip is opposed to the bottom surface of the second recess. A radiation protective film is formed on the main surface other than the circuit formation plane of the IC chip.