A laboratory-purpose submillimeter wavelength receiver is developed and tested. The device can in situ detect the spectrum of an rf source working below 100 K within the frequency range 400-600 GHz. A sample is placed close to the receiver sensor; both are in vacuum inside the probe stick and cooled by liquid helium in the standard transport dewar. The quasioptical sensor design is based on the superconducting integrated receiver chip; its noise temperature below 300 K was measured at /spl ap/500 GHz with a variable-temperature black body. The output level of the tester is suitable for the direct readout by a spectrum analyzer. Details of the design and main test data are reported.