We present the results of experimental development of an ultrasensitive normal metal hot-electron microbolometer with Andreev mirrors and electronic cooling by superconductor- insulator-normal metal (SIN) tunnel junctions. A value NEP equals 5 (DOT) 10-18 W/Hz1/2 for the temperature fluctuations component of noise and the thermal time constant (tau) equals 0.2 microseconds at 300 mK have been estimated for one of the realized devices with thermal conductance G approximately equals 6 (DOT) 10-12 W/K. At 100 mK, the thermal conductance was decreased to G approximately equals 7 (DOT) 10-14 W/K, that gives NEP equals 2 (DOT) 10-19 W/Hz1/2 for the temperature noise component and a thermal time constant (tau) equals 5 microseconds. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.