Each sub word line is coupled to a gate of a transfer transistor of a memory cell. A first switch of a sub word decoder couples the sub word line to a high level voltage line when a main word line is in an activation level. A second switch couples the sub word line to a low level voltage line when the main word line is in an inactivation level. A third switch couples the sub word line to the low level voltage line when a word reset signal line is in an activation level. A reset control circuit disables the inactivation of the main word line or the activation of the word reset signal line during a test mode. One of the second and third switches is forcibly turned off, and thereby, an operation failure of a sub word decoder can be detected easily.