The paper describes an experimental model of a new time-of-flight mass spectrometer suitable for operation in the millisecond time-of-flight range. The ion-optical system of the analyzer is based on plane gridless electrostatic mirrors. To confine an ion beam in the drift direction, a system of five electrostatic lenses is used. The energy focusing range for the analyzer mirror system was determined experimentally and the results appeared to be well correlated with the calculated data. In the course of the analyzer tests, we defined the mirror operating modes at various ion energies, and characterized resolution and transmission as a function of ion energy. The mass spectra taken in the 10 to 100 eV ion energy range show the traces of ions of alkali metals contained in cesium aluminate at levels below 2*10**(-5)  of the cesium ion intensity. The investigations helped to establish specific features of the new analyzer tuning and ion stability limits with respect to external magnetic fields and voltage ripple of power supplies.