Abstract: A method of detecting the status of a keyboard switch device judges validity or invalidity of the status of switching elements on the basis of simple conditions. With this method, processing of output data is facilitated. In a step S1, a scanning operation is carried out to detect the status of each switching element. In a step S2, the result of the scanning operation is stored in a memory unit as memorized information. In a step S3, closed element total number N, a closed row total number Nr, and a closed column total number Nc are counted with reference to the memorized information. In a step S4, a judgement is made as regards whether or not a predetermined condition is satisfied by the closed element total number N, the closed row total number Nr, and the closed column total number Nc. When the predetermined condition is satisfied, the memorized information is provided as valid data in a step S5.