A processing unit of this terminal device communicates with a base station device using an MCG and an SCG, and assesses whether or not to perform wireless link monitoring and/or beam failure detection in the terminal device on the basis of whether an SCG deactivation command transmitted from the base station device contains or does not contain information indicating that wireless link monitoring and/or beam failure detection is to be performed or is not to be performed, and the terminal device determines whether to perform or not to perform wireless link monitoring and/or beam failure detection on the basis of the assessment of whether or not to perform wireless link monitoring and/or beam failure detection.