We experimentally study the transport features of electrons in a spin-diode structure consisting of a single semiconductor quantum dot (QD) weakly coupled to one nonmagnetic and one ferromagnetic (FM) lead, in which the QD has an artificial atomic nature. A Coulomb stability diamond shows asymmetric features with respect to the polarity of the bias voltage. For the regime of two-electron tunneling, we find anomalous suppression of the current for both forward and reverse bias. We discuss possible mechanisms of the anomalous current suppression in terms of spin blockade via the QD-FM interface at the ground state of a two-electron QD.