1. In a computer under control of instructions from a program memory and employing indirect addressing of a data memory included in the computer, where an absolute address to the data memory is derived in an address processing means from a base address which is read from a reference memory in correspondence to an input address to the reference memory and from at least one address parameter which has been stored in a register memory in connection with the execution of an instruction read from the program memory, appartaus for reducing the instruction execution time comprising a buffer memory means for sequentially and temporarily storing in an execution queue instructions read from said program memory, a read-out means for reading base addresses from said reference memory in correspondence to said input address and a read signal, the input address as well as the read signal being derived from an instruction just supplied to said execution queue if the instruction is of a first type which concerns writing or reading in said data memory, a registration means for giving an indication that an instruction which is of a second type that places address parameters in the register memory has been supplied from the output of said buffer memory, a first activation means for initiating transfer of said at least one address parameter from said register memory to said address processing means if said indication is present in said registration means and the instruction being in turn for feed-out to the output of said buffer memory means is of said first type and for removing said indication in the registration means when said transfer has been executed, and a second activation means connected to said address processing means and responsive to a base address which is being read out from said reference memory to said address processing means for initiating the calculation of said absolute address when simultaneously none of the instructions stored ahead of said instruction just supplied to said buffer memory means is of said second type and no indication is present in said registration means.