A computer (10-A) communicably connected to at least one other computer (10-B, 10-C), comprising a at least one processor, a memory, and an interface unit to communicate with the at least one other computer, wherein: the at least one processor, when processing an input or output request in a task that the processor is executing; transmits a request notification including an identifier of the computer, an ID of the task, and an ID of an access target of the request to the at least one other computer (10-B, 10-C); receives from the at least one other computer a request notification transmitted by the at least one other computer; stores, in the memory, contents of the request notification thus received; compares, based on the contents of the request notification received from the at least one other computer and stored in the memory, the request that the processor is trying to process with the request that the processor of the at least one other computer is trying to process; and determines whether or not processing of the request that the processor is trying to process is possible, wherein the at least one processor, when comparing the request that the at least one processor is trying to process with the request that the at least one processor of the at least one other computer is trying to process, determines whether or not an ID of a task equal to the ID of the task that the at least one processor is executing has been received from each at least one other computer; and determines, if there exists a second request which is trying to access an access target equal to an access target of the request that the at least one processor is trying to process, whether or not the at least one processor received the request notification of the second request after receiving the request and based on a result of the comparison, the at least one processor determines whether or not to process the request (S34,S35) the at least one processor, when processing an input or output request in a task that the processor is executing; transmits a request notification including an identifier of the computer, an ID of the task, and an ID of an access target of the request to the at least one other computer (10-B, 10-C); receives from the at least one other computer a request notification transmitted by the at least one other computer; stores, in the memory, contents of the request notification thus received; compares, based on the contents of the request notification received from the at least one other computer and stored in the memory, the request that the processor is trying to process with the request that the processor of the at least one other computer is trying to process; and determines whether or not processing of the request that the processor is trying to process is possible, wherein the at least one processor, when comparing the request that the at least one processor is trying to process with the request that the at least one processor of the at least one other computer is trying to process, determines whether or not an ID of a task equal to the ID of the task that the at least one processor is executing has been received from each at least one other computer; and determines, if there exists a second request which is trying to access an access target equal to an access target of the request that the at least one processor is trying to process, whether or not the at least one processor received the request notification of the second request after receiving the request and based on a result of the comparison, the at least one processor determines whether or not to process the request (S34,S35)