1. A medical device system comprising: a first medical device; a first memory provided in the first medical device; a second medical device; and a second memory provided in the second medical device, wherein the first memory includes a first shared memory area allocated to the first medical device and a second shared memory area allocated to the second medical device, the second memory includes a third shared memory area allocated to the first medical device and a fourth shared memory area allocated to the second medical device, the first medical device includes a first writing unit that dynamically writes, into a certain memory area included in the first shared memory area, definition data that defines a method for using the certain memory area and data corresponding to the definition data, and a first synchronization unit that periodically reads data written into the fourth shared memory area and writes the read data into the second shared memory data, such that data written into the second shared memory area is identical to the data written into the fourth shared memory area, and the second medical device includes a second writing unit that dynamically writes, into a certain memory area included in the fourth shared memory area, definition data that defines a method for using the certain memory area and data corresponding to the definition data a second synchronization unit that periodically reads data written into the first shared memory area and writes the read data into the third shared memory data, such that data written into the third shared memory area is identical to the data written into the first shared memory area.