In a signal processing apparatus, a speech coder includes, as three sections for coding speech data by different algorithm, an Algorithm-A coding section, an Algorithm-B coding section and an Algorithm-C coding section. A noise suppressor includes, as three sections for suppressing background noise by different algorithm, an Algorithm-X noise suppress section, an Algorithm-Y noise suppress section and an Algorithm-Z noise suppress section. A suppress algorithm switching control section controls switching on the basis of information from a coding algorithm switching control section such that an optimal one of the noise suppress sections may function in association with the coding section activated in the speech coder.