The SPICAM IR spectrometer on Mars Express mission (1.0--1.7 ¿m, spectral resolution 0.5--1.2 nm) is dedicated primarily to nadir measurements of H2O abundance. It is one of two channels of SPICAM UV-IR instrument. In this spectrometer we applied for the first time in planetary research the technology of an acousto-optic tunable filter (AOTF) that allowed unprecedented mass reduction for such an instrument: 0.75 kg. SPICAM IR is a point nadir-looking spectrometer with sequential scanning of the spectrum by the AOTF. Sun occultations are performed with a help of dedicated solar port. We describe instrumentation, calibrations, and the modes of operations of the device and discuss its in-flight performances. A brief overview of the scientific measurements includes water vapor measurements and the mapping of intensity of the O2(a1Δg) emission at 1.27 ¿m, described in detail in separate papers. Measurements in reflected solar light allow clear detection of H2O and CO2 ices on the surface or in the atmosphere of Mars. We discuss solar occultation measurements by SPICAM and present resulting vertical profiles of aerosol optical depth.