A spin valve is a microelectronic device in which high-and low-resistance states are realized by using both the charge and spin of carriers. Spin-valve structures used in modern hard-drive read heads and magnetic random access memories comprise two ferromagnetic electrodes whose relative magnetization orientations can be switched between parallel and antiparallel configurations, yielding the desired giant or tunnelling magnetoresistance effect(1). Here we demonstrate more than 100% spin-valve-like signal in a NiFe/IrMn/MgO/Pt stack with an antiferromagnet on one side and a nonmagnetic metal on the other side of the tunnel barrier. Ferromagnetic moments in NiFe are reversed by external fields of approximately 50 mT or less, and the exchange-spring effect(2) of NiFe on IrMn induces rotation of antiferromagnetic moments in IrMn, which is detected by the measured tunnelling anisotropic magnetoresistance(3). Our work demonstrates a spintronic element whose transport characteristics are governed by an antiferromagnet. It demonstrates that sensitivity to low magnetic fields can be combined with large, spin-orbit-coupling-induced magnetotransport anisotropy using a single magnetic electrode. The antiferromagnetic tunnelling anisotropic magnetoresistance provides a means to study magnetic characteristics of antiferromagnetic films by an electronic-transport measurement.