[3] Turning professional in 1998, Kato made his first appearance in an ATP Tour tournament that year, the doubles at the Swiss Open Gstaad with Marco Chiudinelli.

He was twice given a wildcard entry into the men's doubles draw at the Japan Open, the first in 2002, when he partnered with Gouichi Motomura to reach the quarter-finals.

On the other occasion, in 2003, he and Satoshi Iwabuchi upset the top seeded pairing of Wayne Arthurs and Paul Hanley in the first round, en route to the semi-finals.

He played the doubles rubber with Thomas Shimada, which they lost to Mahesh Bhupathi and Leander Paes.

[8] He featured in the main draw of the men's doubles at the 2004 French Open, with Stephen Huss, for a first round exit, to Russians Igor Andreev and Nikolay Davydenko.