To realize toilet environment which is always sanitary and clean by automatically sterilizing a toilet stool and instruments attached to this or the like in connection with the use of a toilet.

A sterilizer for a toilet has a detecting means 6 for directly or indirectly detecting the presence of a user in a toilet room 1 or its circumference and an ozone generating machine 9 for blowing off ozone from ozone blowing off portions 7 and 8 placed within the toilet room 1 and sterilizes a toilet stool 4 and instruments attached to it or the like with ozone by blowing off ozone generated by the ozone generating machine 9 within the toilet room 1 by driving the ozone generating machine 9 when directly or indirectly detecting the presence of a user in the toilet room 1 or its circumference based on a signal from the detecting means 6.