PURPOSE: To speedily carry out installation and exchange of a tool and to carry out high precision machining by measuring tool length in the state of installing the tool on a head and memorizing its correction value.

CONSTITUTION: This tool presetter is furnished with a tool length setting means 35 to set standard tool length, a head to project and support a tool by way of directing the tool downward, a driving means 37 to move the head vertically, a lowering commanding means 36 to issue a lowering command to the driving means 37, a detection means 43 placed on a table below the head and to detect contact of the tool of the head and stop commanding means 42 to input a signal of the detection means 43 and to issue a stop command to the driving means 37. Additionally, a lowering amount measuring means 38 to measure a lowering amount of the head, a tool length computing means 39 to compute a measured value obtained by the lowering amount measuring means 38 into tool length, a tool length correction means 40 to calculate a tool length correction value by way of comparing the tool length obtained by the tool length computing means 39 with standard tool length and a memory means 41 to memorize the correction value obtained by the tool length correction means 40.