An oscillator includes a multi-layered base (101). Circuit patterns (102) are formed on a first main surface and the inside of the multi-layered base (101). Holes (104) through which wiring patterns of the individual layers of the base (101) are connected are formed within the multi-layered base (101). Electronic components (103) are mounted on the first main surface of the multi-layered base (101). First and second reverse electrodes (106, 107), which serve as external terminals to be connected to an external source, are formed on a second main surface of the multi-layered base (101). The first reverse electrode (106) serves as a ground electrode, and the second reverse electrodes (107) serve as terminal electrodes. The reverse electrodes (106, 107) are electrically connected to the circuit patterns (102) via the holes (104). The reverse electrodes (106, 107) are located farther inward than the lateral surfaces of the multi-layered base (101). A shield cover (108) is placed to tightly cover the first main surface of the multi-layered base (101). It is thus possible to provide a miniaturized, less expensive, and easy-to-mount oscillator module in which unwanted radiation characteristics are improved.