Task switching is an important cognitive function when older adults work using ICT equipment. We focused on properties of older adults’ task switching function in order to design usable ICT equipment. Generally, a worker has to execute some tasks serially by switching them reciprocally. In this study, some equences such as AB, AAB, or AAAAB were taken into consideration because there are routine tasks and rare tasks. Participants were 24 older adults and 24 younger adults. Reaction times and switch costs of various sequences were analyzed. As the result, although switch costs for older adults were heavier in AAB than AB, the switch costs did not increase for longer repetition of A (i. e., AAAB and AAAAB). The heaviest switch cost was seen in AAB when A was a difficult task and B was an easy task. These results were different from those of younger adults.