Item values associated with an execution state of a program executed on a computer are collected in detail while suppressing the computer load. When reducing the interval for collecting values of one item to be monitored, the interval for collecting values of items other than that item is increased. If the computer load is increased, an interval of at least one item is increased. Moreover, there is provided an upper limit for the number of items whose intervals can be reduced simultaneously. Moreover, when varying the interval of the item according to the values of the respective items, the interval variation range is varied according to the item state and the computer load.