Disclosed is an oscillator that can be flexibly retrofitted to become usable for a wide range of applications and to become compatible with different users' requests, and that enables a user to design a high-frequency unit using the oscillator without concerns. The oscillator includes a SAW resonator (1) and an oscillation unit (2) provided in the form of an integrated circuit. The SAW resonator and oscillation unit are encapsulated in the same package and then sealed. The whole oscillator is thus provided in the form of a module. The oscillation circuit (4) includes an adjustment terminal (9) with which a current flowing through a current source (8) is adjusted externally. A resistor (R3) offering a desired resistance is connected between the adjustment terminal (9) and a ground terminal (7), whereby a negative resistance can be adjusted. Moreover, an adjustment terminal (10) with which a current flowing through a current source in an amplification circuit (5) is included. A resistor (R4) whose resistance permits an output of a desired intensity is connected between the adjustment terminal (10) and the ground terminal (7). Thus, the intensity of the output can be adjusted.