A processing device may comprise a first controlling unit, a second controlling unit, a first memory and a second memory. The second memory may be set to a normal operation mode in a case where the first controlling unit is in the non-sleeping state, and may be set to a low power consumption mode in a case where the first controlling unit is in the sleeping state. In the case where the first controlling unit is in the sleeping state, the second controlling unit may be configured to perform one of the below processes depending on its condition. If the second controlling unit is to perform a specific process by using a first program, the second controlling unit may perform the specific process on behalf of the first controlling unit by using the first program stored in the first memory while the first controlling unit is maintained in the sleeping state and the second memory is maintained in the low power consumption mode. If the second controlling unit is to perform the specific process by using a second program, the second controlling unit may change a mode of the second memory from the low power consumption mode to the normal operation mode, and perform the specific process on behalf of the first controlling unit by using the second program stored in the second memory, while the first controlling unit is maintained in the sleeping state.