A keyboard musical instrument is provided in which variations in the detection mechanism is corrected so that an appropriate musical sound control can be performed. Detection sections SW1, SW2, and SW3 detect an object at detection positions pSW1, pSW2, and pSW3. On the basis of a detection timing (rT2) by the detection section SW2, a detected key depression speed (V21), and a detection timing (rT3) by the detection section SW3 in a case where the key is depressed in a derivation mode, after a rST32 value is calculated, a stroke correction value calST32 is derived as correction information J and stored in a memory 57. In the performance mode, the musical sound is controlled on the basis of the detection timing by the detection sections SW1, SW2, and SW3 and the stroke correction value calST32.